r 


REESE  LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA 


THE 

PRACTICAL    MANAGEMENT 


OF 


DYNAMOS  AND  MOTORS. 


BY 

FRANCIS    B.    CROCKER, 

it 

PROFESSOR    OF    ELECTRICAL    ENGINEERING,  COLUMBIA    COLLEGE,  NEW  YORK  J  MEMBER   OF  THB 

AMERICAN    INSTITUTE    OF    ELECTRICAL  ENGINEERS  J    PAST    PRESIDENT 

OF  THE   NEW  YORK   ELECTRICAL   SOCIETY; 

AND 

SCHUYLER    S.    WHEELER,    D.Sc., 

ELECTRICAL    EXPERT   OF   THE   BOARD    OF   ELECTRICAL   CONTROL,  NEW    YORK    CITY  J    PAST  VICE 

PRESIDENT   OF  THE  AMERICAN    INSTITUTE   OF   ELECTRICAL    ENGINEERS  ;    MEMBER 

AMERICAN    SOCIETIES    OF   CIVIL   AND    MECHANICAL   ENGINEERS. 


WITH  A  SPECIAL  CHAPTER  BY  H.  A.  FOSTER. 


FOURTH  EDITION,    REVISED   AND   ENj. 
SEVENTH  THOUSAND. 


NEW    YORK: 

D.   VAN    NOSTRAND    COMPANY, 

23  MURRAY  AND  27  WARREN  ST. 

LONDON : 

E.   &  F.    N.  SPON,    125  STRAND. 
1896. 


COPYRIGHT,  1894, 

BY 

D.  VAN  NOSTRAND  COMPANY, 


ROBERT  DRUMMOND,   ELECTROTYPER  AND   PRINTER,   NEW   YORK. 


PREFACE  TO  FIRST   EDITION. 


THE  contents  of  this  book  appeared  as  a  series  of  arti- 
cles in  the  Electrical  Engineer  between  September  1891 
and  May  1892.  Its  object  is  to  give  simple  directions  for 
the  practical  use  and  management  of  dynamos  and  motors. 

The  authors  have  taken  special  care  to  arrange  the  ma- 
terial so  that  the  different  subjects  are  treated  separately 
and  in  the  proper  order,  and  the  headings  are  printed  in 
heavy  type  to  facilitate  ready  reference  to  any  subdivision. 

The  reader  is  recommended  to  familiarize  himself  at 
first  with  the  plan  and  contents  of  the  book,  that  he  may 
when  at  work  be  able  to  turn  readily  to  any  part  required. 

The  authors  design  the  present  volume  to  be  simply  the 
groundwork  of  a  larger  and  more  elaborate  treatment  of 
the  subject  which  they  contemplate  preparing,  and  they  will 
appreciate  any  suggestions. 

NEW  YORK,  May,  1892. 


PREFACE  TO  SECOND  EDITION. 


THE  first  edition  of  this  book  having  been  exhausted  in 
less  than  one  year,  the  authors  have  taken  advantage  of  the 
opportunity  for  revision  and  enlargement  presented  by  the 
issue  of  the  second  edition.  A  few  corrections  and  many 
additions  have  been  made.  As  many  of  the  additions  are 
in  the  chapter  on  examination  and  testing,  and  as  this  is 
properly  a  braftch  by  itself,  it  has  been  separated  as  Part  II. 

Part  IV  has  been  added,  giving  special  instructions  for 
handling  the  Thomson-Houston,  Brush,  and  other  arc-light 
dynamos,  since  these  machines  have  governors  which  re- 
quire additional  directions. 

The  statements  are  directly  based  upon  actual  experi- 
ence, and  most  of  them  have  been  checked  by  the  extensive 
use  of  the  book  by  electrical  teachers,  engineers,  students, 
and  workmen,  not  only  in  college  laboratories  and  the  test- 
ing-rooms of  factories,  but  also  in  the  installation  and  man- 
agement of  dynamos  and  motors  in  commercial  use. 

The  authors  desire  to  acknowledge  the  kindness  and 
assistance  of  several  electric  companies,  and  of  Mr.  Gano  S. 
Dunn,  Engineer  of  the  Crocker- Wheeler  Electric  Company, 
who  has  carefully  examined  the  proofs  and  made  a  number 
of  valuable  suggestions. 

NEW  YORK,  February ',  1894. 


NOTE   ON   THIRD    EDITION. 

A  NUMBER  of  corrections  incidental  to  the  introduction 
of  much  new  matter  in  the  second  edition  have  been  made, 
especially  in  the  chapters  on  the  T.  H.  dynamo,  which  have 
been  carefully  passed  upon  by  Mr.  E.  E.  Boyer,  of  Lynn,  to 
whom  the  authors  wish  to  express  their  thanks. 

NEW  YORK,  October,  1894. 


PART  I. 

DESCRIPTIONS  AND  DIRECTIONS. 

PAGE 

INTRODUCTION <•     n 

CHAPTER  I. 

GENERAL  PRINCIPLES   OF  DYNAMOS   AND   MOTORS. 

Definitions.     Principles  of  Action.    Similarity  of  Dynamos  and  Motors. 

General  Form.     Armature.     Field-magnet 13 

CHAPTER   II. 

SELECTING   DYNAMOS  AND   MOTORS. 

Construction.  Finish.  Simplicity.  Attention  Required.  Handling. 
Interchangeability.  Regulation.  Armature.  Capacity.  Commu- 
tator. Form.  Weight.  Cost 16 

CHAPTER   III. 

CIRCUITS   AND    WINDINGS. 

Electro-metallurgical.  Constant  Potential.  Electric  Railway.  Arc- 
Lighting.  Alternating — Single  Phase — Polyphase 21 

CHAPTER   IV. 

INSTALLING  AND   BELTING  DYNAMOS  AND   MOTORS. 

Setting  up.     Pulleys.     Belting 28 

CHAPTER  V. 

WIRING  AND    CONNECTIONS. 

Connections.  Arranging  Wiring.  Switches  and  Cut-outs.  Diagrams 
of  Connections.  Shunt  Dynamo  supplying  Constant-potential  Cir- 
cuit. Series  Dynamo  supplying  Constant-current  Circuit.  Alter- 
nating-current Plant.  Reversing  Direction  of  Rotation 37 

7 


8  Contents. 

CHAPTER  VI. 

PAGE 

STARTING  DYNAMOS 46 

CHAPTER  VII. 

KINDS   OF  DYNAMOS   AND   SWITCHING   DYNAMOS   INTO   CIRCUIT. 

Dynamos  in  Parallel.  Shunt  Dynamos  in  Parallel.  Series  Dynamos 
in  Parallel.  Compound  Dynamos  in  Parallel.  Alternators  in 
Parallel.  Dynamos  in  Series.  Series  Dynamos  in  Series.  Shunt 
or  Compound  Dynamos  in  Series.  Alternators  in  Series.  Dynamos 
on  the  Three-wire  System 40, 

CHAPTER  VIII. 

KINDS   OF   MOTORS   AND   METHODS   OF  STARTING. 

For  Constant-potential  Circuit:  Shunt- wound  Motor— Series- wound 
Motor — Differentially-wound  Motor.  For  Constant-current  Circuit: 
Series-wound  Motor.  Alternating-current  Motors.  Battery  Motors. 
Dynamotors 63 

CHAPTER   IX. 

RUNNING  DYNAMOS   AND   MOTORS. 

General  Instructions.     Personal  Safety 74 

CHAPTER  X. 

STOPPING   DYNAMOS  AND   MOTORS. 

One  Constant-potential  Dynamo.  Dynamos  in  Parallel.  Compound 
Dynamos  in  Parallel.  Dynamos  on  the  Three- wire  System.  Con- 
stant-current Dynamos  and  Motors.  One  Alternator.  Alternators 
in  Parallel.  Constant-potential  Motor 77 


PART    II. 

EXAMINATION,  MEASUREMENT,  AND    TESTING. 

CHAPTER  XI. 
INTRODUCTION  AND  CLASSIFICATION „  80 

CHAPTER  XII. 

1.  ADJUSTMENT.     2.  MECHANICAL  STRENGTH.     3.  FRICTION.    4.  BAL- 
ANCE.   5.  NOISE.    6.  HEATING.     7.  SPARKING 82 


Contents.  9 

CHAPTER  XIII. 

PAGE 

8.  ELECTRICAL  RESISTANCE  OF  CONDUCTORS  AND  OF  INSULATION  OF 
DYNAMO  OR  MOTOR,  AND  9  OF  CONDUCTOR  AND  OF  INSULATION  OF 
LINE  OR  EXTERNAL  CIRCUIT 88 

CHAPTER   XIV. 

r 

10  VOLTAGE  AND  11  CURRENT „ .  „ .  „ . . . .  „ 98 

CHAPTER  XV. 
12  SPEED  AND  13  TORQUE  OR  PULL „ 103 

CHAPTER  XVI. 
14  POWER  AND  15  EFFICIENCY <„....„,„„.,,...   108 

CHAPTER  XVII. 
16  MAGNETISM  AND  17  SEPARATION  OF  LOSSES „., in 


PART   III. 

THE  LOCALIZATION  AND  REMEDY  OF  TROUBLES  IN 
DYNAMOS  AND  MOTORS. 

CHAPTER  XVIII. 
INTRODUCTION „ . „ » . . .  <> „ .  116 

CHAPTER  XIX. 
SPARKING  AT  COMMUTATOR Oo..... .  120 

CHAPTER  XX. 
HEATING  IN  DYNAMO  OR  MOTOR.     GENERAL  INSTRUCTIONS 132 

CHAPTER   XXL 
HEATING  OF  COMMUTATOR  AND  BRUSHES 134 

CHAPTER   XXII. 
HEATING  OF  ARMATURE „ 136 

CHAPTER   XXIII. 
HEATING  OF  FIELD-MAGNETS. „ 138 


io  Contents. 

CHAPTER   XXIV. 

PACK 

HEATING  OF  BEARINGS 140 

CHAPTER  XXV. 
NOISE 145 

CHAPTER  XXVI. 
SPEED  Too  HIGH  OR  Too  Low „ 150 

CHAPTER   XXVII. 
MOTOR  STOPS  OR  FAILS  TO  START . 152 

CHAPTER   XXVIII. 
DYN-AMO  FAILS  TO  GENERATE. , „ 155 


PART    IV. 

ARC  DYNAMOS  AND  MOTORS  REQUIRING  SPECIAL 
DIRECTIONS. 

CHAPTER   XXIX. 

THOMSON-HOUSTON  ARC   DYNAMO. 

Setting  up  ...............................................  .  .....  ..  .  163 

CHAPTER  XXX. 

THOMSON-HOUSTON   ARC   DYNAMO. 

Troubles  and  Remedies  ...................................  .......*.   181 

CHAPTER  XXXI. 
BRUSH  ARC  DYNAMO..  ....................  .........................  iy<- 


CHAPTER  XXXII. 
FORT  WAYNE,  SPERRY,  AND  EXCELSIOR  ARC  DYNAMOS  .......  ..  .....  197 

CHAPTER   XXXIII. 
ARC  MOTORS  ..........................  .  ..........  ................  203 


PRACTICAL     MANAGEMENT 

OF 

DYNAMOS   AND    MOTORS, 


PART    I. 
Definitions  and    Directions. 


INTRODUCTION. 

THE  purpose  of  this  book  is  to  set  forth  the  more  impor- 
tant facts  which  present  themselves  in  the  actual  handling  of 
dynamo-electric  machines  and  electric  motors,  as  a  guide  for 
those  who  use  or  study  these  machines.  The  authors  do 
not  claim  for  this  treatment  of  the  subject  much  more  than 
that  it  is  a  set  of  directions  in  which  the  various  points  are 
arranged  under  headings  for  convenience  of  reference. 

Heretofore  writers  on  the  dynamo  or  motor  have  usually 
treated  these  machines  entirely  distinctly,  and  books  or 
papers  relating  to  the  dynamo  usually  contain  nothing  about 
the  motor,  or  merely  consider  it  briefly  in  a  few  special  chap- 
ters, and  books  on  the  motor  refer  to  the  dynamo  only  in- 
cidentally. The  authors  have  found  that  there  is  no  neces- 
sity for  this  separation^  in  fact,  nine  out  of  ten  statements 


1 2  Practical  Management  of 

which  apply  to  the  dynamo  are  equally  applicable  to  the 
motor,  and  if  the  word  "  machine  "  is  used  instead,  the  state- 
ment covers  both  and  becomes  doubly  important  and  use- 
ful. Occasionally,  of  course,  it  is  necessary  to  distinguish 
between  the  two  machines,  but,  as  a  matter  of  fact,  the  dif- 
ference in  treatment  required  for  dynamos  and  for  motors  is 
often  less  than  for  different  kinds  of  dynamos ;  for  example, 
a  shunt  dynamo  and  a  shunt  motor  are  much  more  similar 
in  their  construction  and  action  than  a  shunt  dynamo  and  a 
series  dynamo.  The  following  pages  cover  almost  all  types 
of  dynamos  and  motors,  except  that  certain  dynamos  with 
open-coil  armatures,  such  as  the  Thomson-Houston  and 
Brush,  largely  used  for  arc-lighting,  require  special  direc- 
tions to  give  all  the  peculiar  actions  which  may  occur,  par- 
ticularly in  regard  to  sparking.  But  even  with  these  ma- 
chines the  principal  facts,  precautions,  etc.,  are  included  in 
the  general  directions. 

Up  to  the  present  time  the  treatment  of  the  dynamo  and 
the  motor  has  related  almost  entirely  to  theory,  design  and 
construction,  and  little  has  been  written  about  their  opera- 
tion. 

The  theory  and  design  of  the  .dynamo  is  now  one  of  the 
most  interesting  and  perfect  branches  of  applied  science  ;  but 
for  every  one  person  who  builds  dynamos  there  are  a  hun- 
dred who  use  them.  The  authors  have  therefore  confined 
this  book  to  management,  giving  only  a  few  of  the  most  im- 
portant definitions  and  facts  in  the  following  chapter,  and 
they  refer  the  reader  to  existing  works  in  which  the  principles, 
theory,  design  and  construction  of  these  machines  are  very 
ably  and  fully  covered.  The  reader  is  also  referred  to  some 
elementary  work  on  the  principles  of  electricity,  including 
electrical  laws,  phenomena,  units,  methods  of  measurement, 
etc.  These  should  be  thoroughly  learned  before  any  one 
attempts  to  understand  or  handle  electrical  apparatus  of  any 
kind. 


Dynamos  and  Motors. 


CHAPTER  I. 
GENERAL  PRINCIPLES   OF   DYNAMOS   AND   MOTORS. 

Definitions. — A  dynamo-electric  machine  is  a  machine  for 
converting  mechanical  energy  into  electrical  energy  ;  in  other 
words,  it  generates  electric  current  when  driven  by  mechanical 


FIG.  i. — 35-KiLOWATT  CROCKER -WHEELER  DYNAMO.      FOUR-POLE 
COMPOUND-WOUND.     BAR-WOUND  ARMATURE. 

power.  The  term  dynamo-electric  machine  is  so  long  that  it 
is  usually  and  unavoidably  shortened  into  "  dynamo,"  which 
has  exactly  the  same  meaning.  The  name  "  electric  gen- 
erator," or  simply  "  generator,"  is  often  applied  to  the 


14  Practical  Management  of 

dynamo,  especially  when  used  to  produce  current  for  elec- 
tric railway  or  other  motors ;  but  this  distinction  is  merely 
for  convenience.  An  alternating-current  dynamo  is  com- 
monly called  an  "  alternator." 

An  electric  motor  is  a  machine  for  converting  electrical 
energy  into  mechanical  energy ;  in  other  words,  it  produces 
mechanical  power  when  supplied  ^vith  an  electric  current.  An 
electric  motor  is  usually  called  simply  a  motor,  and  although 
motor  might  mean  anything  producing  motion,  it  is  very 
rarely  used  in  any  other  sense,  and  is  perfectly  definite  in 
connection  with  electrical  matters. 

A  dynamotor,  or  motor-dynamo,  is>  as  its  name  implies,  a 
combination  of  the  two  machines,  and  consists  of  a  motor  and 
a  dynamo,  either  directly  coupled  together  or  built  as  one 
machine.  A  dynamotor  is  commonly  used  to  transform  an 
electric  current  of  a  certain  voltage  into  a  current  of  either 
a  higher  or  lower  voltage,  with  a  corresponding  decrease  or 
increase  in  the  number  of  amperes.  Since  these  machines 
are  usually  employed  for  direct  currents  they  are  called  direct 
current  transformers,  but  they  are  often  used  to  convert 
direct  into  alternating  currents,  or  the  converse  ;  they  are 
also  called  rotary  transformers. 

Principles  of  Action. — The  dynamo  is  based  upon  the 
discovery  made  by  Faraday  in  1831,  that  an  electric  current 
is  generated  in  a  conductor  by  moving  the  conductor  in  a 
magnetic  field.  The  electric  motor  works  on  the  principle 
that  a  conductor  carrying  a  current  in  a  magnetic  field  tends 
to  move.  Thus  it  will  be  seen  that  the  dynamo  and  the 
motor  are  exactly  the  reverse  of  each  other  in  their  action. 

Similarity  of  Dynamos  and  Motors. — The  two  ma- 
chines are,  however,  very  similar  in  their  construction.  In 
fact,  the  same  machine  can  be  used  for  either  purpose 
equally  well.  In  practice  dynamos  and  motors  are  some- 
times made  slightly  different,  but  this  is  only  done  to  adapt 
a  machine  more  perfectly  to  a  certain  purpose.  Hence,  as 
already  stated  in  the  introduction,  the  two  machines  will  be 
treated  as  one,  except  where  some  distinction  is  specially 
stated. 


Dynamos  and  Mottfrs^ .  ^^          15 


General  Form. — We  have  seen  that  both  the  dynamo 
and  motor  depend  for  their  action  upon  the  movement  of 
conductors  in  magnetic  fields.  Now  it  has  been  found  as  a 
result  of  scientific  experiment  and  practical  experience  dur- 
ing the  60  years  since  Faraday's  discovery,  that  the  best  way 
to  carry  out  this  principle  is  to  arrange  the  conductors  in 
suitable  form  and  rotate  them  between  the  poles  of  a  magnet, 
or  magnets.  This  rotating  part  is  called  the  armature  and 
the  magnet  is  called  t\\Q  field-magnet.  In  alternating-current 
dynamos  this  plan  is  sometimes  reversed,  the  field-magnets 
being  made  to  rotate  and  the  armature  being  fixed. 

Armature. — This  usually  consists  of  an  armature  core  of 
iron,  on  which  are  wound  or  fastened  the  conductors  which 
carry  the  current.  This  iron  core  should  be  split  up  or 
laminated ;  that  is,  made  of  discs,  tape,  or  wire,  separated  by 


FIG.  2.— i  H.  P.  SCO-VOLT  ARMATURE,  WIRE-WOUND. 

paper,  varnish,  or  rust,  instead  of  one  solid  piece  ;  otherwise 
it  will  have  useless  ("  Foucault  ")  currents  generated  in  it, 
which  would  waste  the  power  of  the  machine.  This  core  is 
almost  always  made  either  in  the  form  of  a  drum  or  a  ring, 
and  hence  we  have  these  as  the  two  principal  types  of 
armature. 

Field-magnet. — This  consists  of  one  or  more  iron  cores, 
on  which  are  wound  the  field^A.  Attached  to  the  field- 
cores  are  the  pole-pieces,  which  give  form  to  the  magnetic 
field,  or  space  in  which  the  armature  revolves. 


1 6  Practical  Management  of 


CHAPTER    II. 
DIRECTIONS  FOR   SELECTING  DYNAMOS  AND  MOTORS. 

THE  choice  of  a  dynamo  or  motor  will,  of  course,  depend 
largely  upon  the  circumstances  in  each  particular  instance. 
There  are,  however,  certain  general  principles  which  apply 
to  almost  all  cases. 

Construction. — This  should  be  of  the  most  solid  char- 
acter and  first-class  in  every  respect,  including  material  and 
workmanship,  both  of  which  should  be  of  the  best  possible 
quality.  All  the  parts  should  be  of  adequate  size  and 
strength  to  insure  durability. 

Finish. — A  good  finish  is  desirable — first,  because  it 
indicates  good  construction,  both  being  secured  by  care  and 
repeated  improvements ;  second,  because  it  stimulates  the 
interest  and  pride  of  the  attendant;  and,  third,  because  it 
shows  the  least  dirt  or  neglect. 

Simplicity. — The  machine  and  all  its  parts  should  be  as 
simple  as  possible,  and  any  very  peculiar  or  complicated 
part  or  attachment  should  be  avoided.  These  are  some- 
times successful,  but  should  be  well  tried  and  proved  before 
being  accepted. 

Attention. — The  amount  of  attention  required  by  the 
machine  should  be  small;  for  example,  the  brushes  should 
be  capable  of  being  easily  and  securely  adjusted,  and  the 
oiling  devices  should  be  effective  and  reliable,  self-oiling 
bearings  being  very  desirable.  The  screws,  connections, 
and  other  small  parts  should  be  arranged  so  that  they  are 
not  liable  to  become  loose,  and  the  delicate  parts  should 
not  be  particularly  exposed  or  liable  to  injury.  The 
machine  should  be  made  so  as  to  be  easily  and  thoroughly 
cleaned. 


Dynamos  and  Motors.  1  7 

Handling.  —  The  machine  should  be  provided  with  an 
eye-bolt  or  other  means  by  which  it  can  be  easily  lifted  or 
moved  without  injury.  It  should  be  possible  to  take  out 
the  armature  conveniently  by  removing  one  of  the  bearings, 
or  the  top  of  the  field-magnet. 

Intel-changeability.  —  Machines  should  be  made  with 
interchangeable  parts,  so  that  a  new  piece  which  will  fit 
perfectly  can  be  readily  obtained  (Fig.  3)  ;  for  this  reason 
regular  and  established  types  of  machine  are  preferable  to 
special  or  unsettled  forms. 

Regulation.  —  Some  form  of  regulator  should  be  pro- 
vided by  which  the  E.  M.  F.  or  current  of  a  dynamo  or  the 
speed  of  a  motor  can  be  reliably  and  accurately  governed. 

Armature.  —  This  should  turn  very  freely  in  the  bear- 
ings, and  should  be  perfectly  balanced,  so  as  not  to  have  any 
appreciable  jar  or  vibration  at  full  speed.  There  should  be 
a  uniform  clearance  of  at  least  -J-  inch  all  around  between 
the  armature  and  pole-pieces.  The  armature  should  be 
capable  of  moving  lengthwise  in  the  bearings  at  least  \  inch, 
except  in  the  case  of  those  types  of  machine  in  which  the 
armature  would  strike  the  pole-pieces  if  it  moved  longi- 
tudinally. It  is  not  usually  desirable  to  have  the  speed  of 
an  armature  at  its  circumference  more  than  three  thousand 
feet  per  minute.  The  ring  form  of  armature  is  especially 
suited  to  high  voltage,  since  the  coils  differing  most  in  po- 
tential are  at  the  greatest  distance  apart.  A  section  can 
also  be  more  easily  rewound  on  a  ring  than  on  an  ordinary 
drum  armature. 

Capacity.  —  This  should  be  ample  in  all  cases.  It  is  a 
very  common  mistake  to  underestimate  the  work  required  of 
a  given  machine,  and,  even  if  the  machine  has  sufficient 
power  at  first,  the  demands  upon  it  are  apt  to  increase  and 
finally  overload  it.  No  one  is  ever  likely  to  regret  choosing 
a  dynamo  or  motor  with  a  considerable  margin  of  capacity, 
since  these  machines  only  consume  power  in  proportion  to 
the  work  they  are  doing.  For  example,  a  25  H.  P.  machine 
would  probably  run  with  a  20  H.  P.  load  moreeconomically 


OF   THE 

UNIVERSITY 


i8 


Practical  Management  of 


Dynamos  and  M^/^s^C^ufQ^^^         19 


and  satisfactorily  than  a  20  H.  P.  machine  with  the  same 
load. 

Commutator. — This  should  be  large  enough  to  radiate 
the  heat  produced  by  the  current  and  by  friction  of  the 
brushes,  and  it  should  have  a  sufficient  number  of  bars  so 
that  the  difference  of  potential  between  adjacent  ones  shall 


FIG.  4.— COMMUTATOR. 

not  be  excessive.  Nothing  but  mica  insulation  should  be 
used  between  the  bars  except  in  the  case  of  certain  arc- 
lighting  machines  with  very  few  segments,  which  have  about 
J  inch  air-space  between  the  bars. 

Form. — The  machine  should  be  symmetrical,  well  pro- 
portioned, compact  and  solid  in  form.  If  it  is  either  very 
tall  or  very  flat  it  is  usually  inconvenient  and  clumsy.  No 
part  of  the  machine  should  project  excessively,  or  be  awk- 
wardly formed  or  arranged.  The  large  and  heavy  por- 
tions of  the  machine  should  be  placed  as  low  as  possible  to 
give  great  stability.  For  the  same  reason  the  shaft  should 
not  be  high  above  the  base,  nor  should  it  be  so  low  that 
there  is  not  ample  room  for  the  pulley  or  other  attachment. 
A  horizontal  belt,  for  example,  will  sag  and  strike  the  floor 
if  the  pulley  is  very  low. 

Weight. — The  common  idea  that  it  is  desirable  to  have 
a  very  light  dynamo  or  motor  is  a  mistake  when  it  is  for 
stationary  use.  There  is  no  advantage  in  a  light  machine 
for  stationary  work,  and  it  has  the  disadvantages  of  being 


20  Practical  Management  of 

less  strong,  less  durable,  and  less  steady  in  running.  A 
sufficient  weight  to  make  the  machine  thoroughly  substan- 
tial is  obviously  a  great  benefit. 

Cost. — It  is  also  a  mistake  to  select  a  cheap  machine, 
since  both  the  materials  and  workmanship  required  in  a 
high-quality  dynamo  or  motor  cost  more  than  in  almost  any 
other  machine  of  the  same  size  and  weight.  It  is  an  unde- 
niable fact  that  there  has  been  considerable  trouble  and  loss 
with  electrical  machinery,  owing  to  inferior  construction. 

These  suggestions  as  to  selecting  a  dynamo  or  motor 
may  be  followed  when  it  is  possible  to  make  only  a  general 
examination  of  the  machine,  or  even  in  cases  where  it  is 
only  possible  to  obtain  a  drawing  or  description  of  it.  If  it 
is  desired  to  make  a  complete  investigation  of  the  machine, 
it  is,  of  course,  necessary  to  make  a  thorough  test  and 
measure  exactly  its  various  constants.  This  can  be  done  as 
completely  as  may  be  required  by  following  the  "  Directions 
for  Testing,"  which  are  given  in  Part  II. 

A  satisfactory  test  cannot  usually  be  made,  however, 
until  after  the  machine  is  set  up  in  place  ;  and,  moreover, 
it  is  not  generally  necessary  if  the  machine  is  obtained  from 
a  reputable  source. 


Dynamos  and  Motors. 


21 


CHAPTER   III. 

CIRCUITS   AND   WINDINGS. 


The  Various  Kinds  of  Circuits  on  which  motors  and 
dynamos  are  commonly  used,  and  the  best  type  of  machine 
in  each  case,  are  as  follows : 

DIRECT   CURRENT,    CONSTANT    POTENTIAL. 

(Circuits  on  which  potential  or  voltage  is  kept  constant,  machines,  lamps,  etc., 
being  run  in  parallel. ) 


Circuits 
iatended  for  — 

Potential. 

Dynamo 
should  be  — 

Motor 
should  be  — 

Electrometal- 

i  to  150  volts 

Shunt  wound. 

Not  used. 

Incandescent 

f    1  10  volts    1 
I  (2-wire  sys.)  1 
j     220  volts     j 

Shunt  or  compound 

Shunt  wound  for  con- 
stant speed. 
Sometimes  series  or 

Electric  railway.  . 
Electric  power.  .  . 

L(3-wiresys.)j 
I  500  volts,   j 

wound. 

Shunt  or  compound 
wound. 

compound  wound  for 
very  variable  speed. 

Series  wound  for 
railway. 
Shunt  wound  for 
stationary. 

DIRECT,    CONSTANT    CURRENT. 

(Circuits  on  which  current  or  amperes  are  kept  constant,  machines,  lamps,  ete. 
being  run  in  series.) 


Circuits 
intended  for— 

Current 
in  Amperes. 

Dynamo 
should  be  — 

Motor 
should  be  — 

Arc-lighting  
Power  circuits.  .  . 

]           6.8 

\         9-5 
or 
j        18. 

Series  wound 
with  current 
regulator. 

Series  wound 
with  speed- 
regulator. 

22 


Practical  Management  of 


ALTERNATING   CURRENT,    SINGLE   PHASE. 
{Almost  always  constant  potential.') 


Circuits 
intended  for  — 

Potential 
in  Volts. 

Dynamos 
should  be  — 

Motor 
should  be  — 

Incandescent 
licrhtincr 

Primary, 
1000  or  more. 
{Not  in  ex- 
tensive 
use. 

Secondary, 
50  or  100. 

Separately 
excited. 
Also  some- 
times com- 
pound wound 

Specially 
designed. 

Arc-lighting 

Sometimes  constant  current 

Electric  power.  .  . 

ALTERNATING    CURRENT,    POLYPHASE. 

{Constant  potential,  two  or  three  phase  currents.) 


Circuits 
intended  for  — 

Potential 
in  Volts. 

Dynamos 
should  be  — 

Motor 

Power  transmis- 

On  the  line, 
5000  to  20000- 

In  the 
machines, 
50  to  100. 

Separately 
excited. 

Either  of 
synchronous 
or  induction 
type  (the  latter 
has  no  com- 
mutator or 
other  electrical 
connection  to 
moving  parts. 

Kinds  of  Circuits. — There  are  really  only  five  classes  of 
electric  circuits  in  very  general  use. 

I.  Electrometallurgical  Circuits,  on  which  the  potential 
is  usually  very  low,  being  only  3  to  6  volts  for  electroplat- 
ing. In  the  electrolytic  refining  of  copper  the  voltage  is 
sometimes  about  100  where  there  are  a  large  number  of 
vats  in  series.  On  the  low-voltage  circuits  the  current  is 
usually  very  great,  being  often  several  thousand  amperes. 

The  dynamos  should  be  simple  shunt  wound  to  give  a 
direct  current  of  the  required  voltage,  and  regulated  by 
means  of  a  rheostat  in  the  field-circuit.  Motors  are  rarely 
used  on  these  circuits,  but  a  shunt  or  series  wound  motor 
could  be  run  if  desired  in  the  same  way  as  upon  the  cir- 
cuits described  in  the  following  paragraph. 


Dynamos  and  Motors.  23 

2.  Low  (Constant)  Potential  Direct  Current  Circuits  for 

light  and  power  are  either  two  wire  (Fig.  1 8)  or  three  wire 
(Fig.  32).  On  the  former  the  potential  is  kept  constant 
and  between  no  and  125  volts,  the  current  being  about  one 
half  ampere  per  16  candle-power  lamp  and  about  8  amperes 
per  horse-power  of  motors  in  operation.  (A  standard  of  80 
volts  is  adopted  in  the  navy.) 

The  voltage  on  the  three-wire  system  is  twice  as  great, 
or  220  to  250  volts,  and  the  current  one  half,.  The  two-wire 
system  is  almost  universally  used  for  light  and  power  distribu- 
tion, when  the  distance  of  the  lamps  or  motors  from  the 
dynamos  is  not  more  than  one-quarter  to  one-half  mile.  The 
three-wire  system  being  employed  where  the  average  distance 
is  greater,  but  not  more  than  one  to  two  miles. 

Shunt  or  compound  wound  dynamos  generating  115  to 
125  volts  are  used  on  either  the  two  or  three  wire  systems, 
two  dynamos  being  run  in  series  in  the  latter  case  (Fig.  32). 
A  single  dynamo  or  pair  of  dynamos  are  used  in  small 
plants,  and  a  dozen  or  more  in  large  plants.  It  is  always 
well  to  have  one  or  more  reserve  machines. 

Motors  for  the  two-wire  system  should  be  plain  shunt  or 
compound  wound  for  115  to  120  volts  (5  or  10  volts  being 
lost  on  the  line)  and  for  the  three  wire  they  should  be 
wound  for  230  to  240  volts.  Series-wound  motors  are 
sometimes  used  for  elevator,  fan,  pump  or  other  work, 
where  there  is  no  danger  of  the  load  being  taken  off  (by  the 
breaking  of  the  belt,  for  example)  which  might  allow  them 
to  "  race  "  and  destroy  themselves.  Compound-wound 
motors  are  adapted  to  work  at  variable  speeds,  such  as  is 
necessary  in  hoisting-apparatus,  and  they  have  the  advan- 
tage that  the  shunt  portions  of  their  field-winding  prevents 
them  from  racing. 

Five-wire  systems  of  about  450  volts  are  in  use  in 
Europe,  but  they  are  complicated,  and  have  never  been 
introduced  in  America. 

3.  Electric  Railway  Circuits  are  almost  always  oper- 
ated at    a    nominally  constant    potential  of   500  volts,  but 
varying  in  practice  between  450  and   550  volts.     The  aver- 
age current  is  about  15  to  25  amperes  per  car.     Stationary 


24  Practical  Management  of 

*  electric  motors  are  very  often  supplied  with  current  from 
electric-railway  circuits.  They  should  be  shunt  wound  or 
"  overwound  series  "  for  500  volts  nominal,  but  capable  of 
standing  at  least  550,  and  should  be  particularly  well  made 
and  insulated.  Special  "  power  circuits  "  of  500  volts  are 
often  used  for  supplying  stationary  motors  only.  These  are 
similar  to  railway  circuits,  except  that  the  current  is  stead- 
;er. 

4.  Series  Arc-lighting  Circuits  are  usually  run  at  a  con- 
stant current  of  about  10  amperes,  the  potential  being 
about  50  volts  per  lamp  on  10  ampere-circuits.  The  total 
voltage  is  usually  2000  or  3000,  40  or  60  lamps  being  con- 
nected in  series,  as  shown  in  Fig.  19.  Arc  circuits  of  7  and 
20  amperes  are  sometimes  used.  The  series  system  is  used 
for  arc-lighting  where  the  lamps  are  very  much  scattered,  the 
length  of  the  circuits  sometimes  being  as  great  as  10  or  15 
miles.  Formerly  this  system  was  almost  invariably  adopted 
for  arc-lighting,  but  now  arc-lamps  are  often  put  on  the  low- 
tension  circuits,  previously  described,  when  the  distances  do 
not  exceed  those  there  stated. 

Series-wound  motors  are  operated  on  arc  or  constant 
current  circuits,  but  they  should  be  provided  with  an  effect- 
ive governor  or  cut-out,  to  prevent  the  speed  from  becom- 
ing excessive  if  the  load  is  likely  to  be  reduced  or  taken  off. 
(See  page  203.) 

A  great  many  types  of  these  machines  have  been  devised, 
but  while  there  are  a  great  many  in  use,  they  are  not  as  ex- 
tensively used  as  the  plain,  constant  potential  motors.  Satis- 
factory results  have  been  obtained,  particularly  in  driving 
fans  or  other  steady  load  ;  but  a  very  variable  load  requires 
too  much  action  on  the  part  of  the  governor  and  tends  to 
cause  sparking.  In  short,  motors  on  constant  current  cir- 
cuits do  not  usually  work  as  well  as  those  on  constant 
potential  circuits,  principally  because  it  is  difficult  to  govern 
the  speed  of  the  former,  whereas  a  simple  shunt  motor  runs 
at  almost  perfectly  constant  speed  on  u  constant  potential 
circuit,  in  spite  of  variations  in  load.  Constant  current  or 
arc-dynamos,  on  the  other  hand,  are  thoroughly  practical 
machines,  and  there  are  several  very  good  types  in  exten- 


Dynamos  and  Motors. 


u=, 

I 


26  Practical  Management  of 

sive  use;  in  fact,  it  was  these  machines  which  first  brought 
electric-lighting  into  general  use. 

5.  Alternating-current  Circuits  are  generally  adopted 
for  supplying  incandescent  lights,  in  cases  where  the  distance 
of  the  lamps  exceeds  one  mile,  or  where  the  low-tension  sys- 
tem is  not  applicable.  The  great  advantage  of  the  alternating 
current  is  that  it  can  be  transformed  into  a  current  of  higher 
or  lower  pressure  by  a  simple  apparatus  containing  no  moving 
parts.  This  makes  it  practical  to  distribute  the  current  at  high 
potential,  usually  1000  volts,  through  wires  which  maybe  small 


FIG.  6. — SMALL  ALTERNATING-CURRENT  FAN  MOTOR. 

because  the  amperes  are  correspondingly  less.  This  cur- 
rent is  changed  at  desired  points  by  means  of  suitable  trans- 
formers into  currents  of  50  or  100  volts,  for  feeding  the 
lamps.  (See  Fig.  20.)  The  complication  and  cost  of  trans- 
formers, danger  to  life,  and  the  difficulty  of  insulation  of 
high-tension  systems  must,  however,  be  considered. 

An  alternating-current  dynamo  (Fig.  5)  possesses  the  ad- 
vantage of  having  a  pair  of  simple  collecting  rings  instead  of 


OF   THE 

UNIVERSITY 
Dynamos  and  Motor  s\. 


a  commutator,  and  may  thus  be  easily  distinguished  from 
a  direct-current  machine.  An  alternator  usually  requires  a 
small  direct-current  dynamo  to  separately  excite  its  field- 
magnets.  Sometimes  alternators  are  made  self-exciting  by 
having  the  current  generated  by  a  portion  of  their  armature 
coils  converted  into  a  direct  current  by  means  of  a  commu- 
tator. These  machines  are  also  made  compound  wound  or 
•"  composite  "  by  rectifying  by  a  commutator  the  main  cur- 
rent or  a  current  induced  by  it.  Alternating-current  motors 
have  not  yet  been  used  in  large  numbers.  Considerable 
difficulty  has  been  found  in  constructing  motors  to  operate 
well  on  the  ordinary  single-phase  (two-wire)  circuits.  Small 
motors  of  this  kind,  however,  are  quite  extensively  used  for 
driving  fans,  Fig.  6,  and  several  types  of  larger  motors  have 
been  brought  out,  but  they  are  not  yet  in  very  general  use. 
Motors  as  well  as  dynamos,  for  two-  and  three-phase  alter- 
nating currents,  are  very  perfect  machines  ;  but  at  present  the 
necessary  circuits  have  not  been  widely  introduced.  The 
purpose  to  which  these  poly-phase  currents  are  particularly 
applicable  is  the  long-distance  transmission  of  power.  An 
enormous  plant  of  this  kind  is  now  being  installed  at  Niagara 
Falls. 


28 


Practical  Management  of 


CHAPTER  IV. 

DIRECTIONS  FOR  INSTALLING  AND  BELTING  DYNAMOS 
AND  MOTORS. 

Setting  up. — The  place  selected  for  a  dynamo  or 
motor  should  be  dry,  clean,  cool,  away  from  all  pipes  if 
possible,  where  the  machine  is  in  plain  sight,  and  has  plenty 
of  room  on  all  sides  for  easy  access.  It  must  be  located  so 
there  is  room  enough  to  take  out  its  armature.  Avoid  par- 
ticularly any  dusty,  wet,  or  hot  location.  Any  place  near 
which  grinding,  filing,  turning,  or  similar  work  is  likely  to  be 
done  is  very  undesirable  for  a  dynamo  or  motor,  as  the 
dust  and  chips  produced  are  liable  to  injure  the  bearings, 
commutator,  and  insulation  of  the  machine.  A  firm  and 
level  foundation  should  be  provided  in  any  case,  and 
machines  of  20  H.  P.  or  more  should  be  set  on  solid  stone, 
brick,  or  timber  foundations  (Fig.  7). 


FIG.  7.— BRICK  FOUNDATION. 

Foundations  for  machinery  should,  if  possible,  be  separate 
from  the  foundations  or  walls  of  the  building,  in  order  to 
avoid  transmitting  any  vibration,  which  is  sometimes  very 
annoying.  It  is  well,  particularly  in  the  case  of  high-voltage 
machines,  to  have  them  placed  upon  an  insulating  base- 
frame  of  wood,  the  pores  of  which  should  be  filled  with  par- 


Dynamos  and  Motors. 


29 


affine  or  well  varnished  to  keep  out  moisture.     If  a  wooden 
belt-tightening   base  is    used,  it   will    answer    this   purpose 


FIG.  8. — BELT-TIGHTENING  WOODEN  BASE-FRAME. 

(Fig.  8);  but  if  iron  tracks  are  used,  they  should  be  placed  on 
a  wooden  base. frame. 

In  unpacking  and  putting  the  machines  together  the 
greatest  possible  care  should  be  used  in  avoiding  the  least 
injury  to  any  part,  in  scrupulously  cleaning  each  part,  and  in 
putting  the  parts  together  in  exactly  the  right  way.  This 
care  is  particularly  important  with  regard  to  the  shaft,  bear- 
ings, magnetic  joints  and  electrical  connections,  from  which 
every  particle  of  grit,  dust,  chips  of  metal,  etc.,  should  be 
removed.  It  is  very  desirable  to  have  machinery  put  to- 
gether by  a  person  thoroughly  familiar  with  its  construc- 
tion, and  in  the  absence  of  such  a  person  no  one  should 
attempt  it  without  at  least  a  drawing  or  photograph  of  the 
complete  machine  as  a  guide.  An  exception  may  be  made 
to  this  rule  if  the  machine  is  very  simple  and  the  way  to 
put  it  together  is  perfectly  obvious,  but  in  no  event  should 
the  installation  or  management  of  machinery  be  left  to 
guess-work.  The  armature  should  be  handled  with  the 
greatest  possible  care,  in  order  to  avoid  injury  to  the  wires 
and  their  insulation,  as  well  as  to  the  commutator  and  shaft 
Handle  and  support  the  armature  as  far  as  possible  by  the 


30  Practical  Management  of 

shaft,  and  avoid  any  strain  on  the  armature-body  or  commu- 
tator. If  it  is  necessary  to  lay  the  armature  on  the  ground 
interpose  a  pad  of  cloth;  but  it  is  much  better  to  rest  the 
shaft  on  two  wooden  horses  or  other  supports.  A  con- 
venient form  of  sling  for  handling  armatures  is  shown  in 
Fig.  9. 


FIG.  9.— SLING  FOR  HOISTING  ARMATURE. 

The  bearings  should  be  very  carefully  cleaned,  set  in  ex« 
actly  the  right  position,  and  firmly  screwed  in  place.  The 
shaft  should  then  revolve  perfectly  freely.  The  rings  of 
self-oiling  bearings  and  other  oiling  devices  should  be 
examined  to  see  that  they  are  adjusted  to  work  properly 
(Fig.  10). 

Pulleys. — A  dynamo  or  motor  usually  has  a  pulley 
suited  to  it,  furnished  by  the  maker.  In  the  case  of  a 
dynamo,  do  not  use  a  smaller  pulley,  and  with  a  motor  do 
not  use  a  larger  one  without  consulting  a  competent  electri- 
cal engineer,  because  either  of  these  changes  would  increase 
the  work  of  the  machine.  The  size  of  pulley  required  on 
the  other  machine  or  counter-shaft,  to  which  the  given 


Dynamos  and  Motors.  31 

machine  is  to  be  connected,  is  found  by  multiplying  the  revo- 
lutions per  minute  of  the  dynamo  or  motor  by  the  diame- 
ter of  its  pulley  expressed  in  inches  and  dividing  by  the  revo- 
lutions per  minute  of  the  other  shaft,  which  gives  diameter 
of  pulley  in  inches.  The  proper  speed  for  a  dynamo  or  motor 
should  always  be  obtained  from  its  manufacturers,  and  this 
speed  should  not  be  departed  from  without  their  approval. 
It  is  commonly  stamped  on  the  name-plate  of  the  machine 


FIG.   io.— DETAIL  OF  SELF-OILTNG  BEARING. 

or  written  on  a  card  packed  with  it.  A  simple  way  of 
determining  the  sizes  or  speeds  in  any  belt  or  gear  trans- 
mission is  to  remember  that  the  speed  of  either  pulley  or 
gear-wheel  of  a  pair  multiplied  by  its  diameter  is  equal  to 
the  speed  of  the  other  multiplied  by  its  diameter.  An 
allowance  should  be  made  for  two  or  three  per  cent  loss  of 
speed  in  the  driven  pulley  owing  to  the  slip  of  the  belt.  In 
fact,  the  usual  result  is  that  the  speed  actually  obtained  in 
practice  is  less  than  is  expected,  and  this  often  makes  a 
change  of  pulleys  necessary. 

Belting. — The  kind  of  belting  to  be  selected  is  somewhat 
a  matter  of  taste,  but  "  light-double  "  leather  belting  is  appli- 
cable to  most  cases,  and  is  generally  satisfactory.  The  width 
of  belting  is  usually  made  about  one  inch  less  than  the 


3  2  Practical  Management  of 

face  of  the  pulley  on  the  dynamo  or  motor.  The  common 
rule  for  determining  width  of  belt  is  that  "  single  "  belt  will 
transmit  I  H.  P.  for  each  inch  in  width  at  a  speed  of  1000 
feet  per  minute.  Jf  the  speed  is  greater  or  less,  the  power 
is  correspondingly  increased  or  decreased. 

This  is  based  upon  the  condition  that  the  belt  is  in  con- 
tact with  the  pulley  around  one  half  of  its  circumference  or 
1 80°,  which  is  usually  the  case.  If  the  arc  of  contact  is  less 
than  half  a  circle  the  power  transmitted  is  less  in  the  follow- 
ing proportion  :  An  arc  of  contact  of  135°  or  three  eighths  of 
the  whole  circumference  gives  .84,  while  90°  or  one  quarter 
of  the  circle  gives  only  .64  of  the  power  derived  from  a  belt- 
contact  around  one  half  of  the  circle. 

If,  on  the  other  hand,  the  upper  side  of  the  belt  sags 
downward,  as  should  always  be  the  case,  and  the  belt  is  in 
contact  with  more  than  half  of  the  circumference  of  the 
pulley,  then  the  "grip  "  is  considerably  increased,  the  belt 
acting  on  the  principle  of  a  strap-brake.  The  greatly  in- 
creased power  that  can  be  transmitted  when  the  belt  thus 
surrounds  more  than  half  of  the  pulley  makes  it  very  desir- 
able to  have  the  loose  side  of  the  belt  on  top.  If  the  loose 
side  is  below,  it  sags  away  from  the  pulleys,  and  is  also  apt 
to  strike  the  floor. 

The  complete  formula  is  H.  P.  =  WX  SX  C ;   that  is, 

1000 

the  horse-power  transmitted  by  a  "  single  "  belt  is  equal  to 
the  width  of  belt  in  inches  (W)  multiplied  by  the  speed  of 
belt  in  feet  per  minute  (S),  and  by  the  figure  depending 
upon  the  arc  of  contact  (C),  and  divided  by  1000.  For  ex- 
ample, a  belt  six  inches  wide  travelling  at  1500  feet  per 
minute  and  touching  three  eighths  of  the  circumference  of 
the  pulley  will  transmit : 

6x  1500  X  .84  =  7560  _  R    p 

1000  IOOO 

"  Double  "  belting  is  expected  to  transmit  one  and  one 
half,  and  "  light  double  "  one  and  one  quarter  times  as  much 
power  as  "  single  "  belting.  Another  rule  for  calculating  the 


Dynamos  and  Motors.  33 

power  that  a  single  belt  will  convey  is  that  75  sq.  ft.  per 
minute  passing  over  the  pulley  transmits  one  H.  P. 

Rope-belting  is  employed  more  than  leather  in  Europe, 
and  is  now  used  a  little  in  America.  Its  advantages  are 
lightness,  cheapness,  quietness,  and  large  capacity  in  small 
space.  It  is  particularly  suited  to  cramped  locations,  a 
number  of  turns  being  used  around  both  pulleys  ;  and  to 
very  long  distances,  for  example,  between  separate  build- 
ings, where  a  long  single  rope  is  used. 

Cotton  or  hemp  rope,  from  one  to  two  inches  in  diameter, 
is  used,  running  in  V-grooves  of  about  45°,  which  wedges  the 
rgpe  and  gives  a  good  grip.  A  very  long  even  splice  is 
required.  When  several  ropes  running  side  by  side  are  em- 
ployed they  may  be  entirely  separate  and  complete  belts,  or 
one  long  one  making  several  turns,  in  which  case  the  rope 
is  crossed  over  from  the  last  groove  to  the  first  by  a  slant- 
ing idler  pulley,  which  serves  also  as  a  belt-tightener.  The 
capacity  is  from  5  to  10  H.  P.  per  one-inch  rope  at  3000  feet 
per  minute,  which  is  the  usual  speed.  The  power  of  rope 
belting  increases  as  the  square  of  its  diameter. 

Rubber  belt  has  50  %  more  adhesion  than  leather. 
Rubber  stretches  continuously.  For  new  leather  allow 
one  quarter  to  one  half  inch  per  foot  for  stretching.  Belts 
slip  or  "  creep  "  on  the  pulley  about  two  per  cent  ;  hence 
in  determining  size  of  pulleys  when  speed  must  be  accurate, 
arrange  them  to  make  the  calculated  speed  two  per  cent 
too  high. 

The  smooth  side  of  a  belt  should  be  run  against  the 
pulley,  as  it  transmits  more  power  and  wears  better.  An 
endless  belt  should  be  used  for  dynamos  and  motors,  since 
they  usually  run  at  high  speeds.  When  belts  are  joined  or 
spliced  while  inposition  on  the  pulleys,  which  is  often  ne- 
cessary, some  form  of  belt-clamp  is  required,  such  as  is  shown 
in  Fig.  ii. 

The  belt  is  stretched  very  tight  with  this,  and  the  ends 
are  held  in  position,  overlapping  each  other  by  the  clamp. 
Both  ends  are  previously  pared  down  with  a  sharp  knife 
till  they  are  the  shape  of  a  long,  thin  wedge,  so  that  when 
laid  together  a  long,  uniform  joint  is  formed  of  no  greater 


34  Practical  Management  of 

thickness  than    the  belt  itself.     The  parts  are  then  firmly 
joined  by  cement  and  rivets. 

If  an  endless  belt  is  not  used  the  joint  should  be  very 
carefully  laced,  so  as  to  make  it  as  straight  and  smooth  as 
possible-  In  lacing-belts  there  must  always  be  as  many 


FIG.  ii. — CLAMP  FOR  STRETCHING  BELT  AND  HOLDING 
ENDS  WHILE  MAKING  JOINT. 

stitches  of  the  lacer  slanting  to  the  left  as  there  are  to  the 
right.  Otherwise  the  ends  of  the  belt  will  shift  sideways, 
owing  to  the  unequal  strain,  and  the  projecting  corners  will 
catch  on  something.  Two  good  ways  of  doing  this  are 
shown  in  Fig.  12.  In  plan  A  two  rows  of  oval  holes  should 
be  made  with  a  punch,  as  indicated.  The  nearest  hole 
should  be  £  inch  from  the  side,  and  the  first  row  -J  inch 
from  the  end,  and  the  second  row  if  inches  from  the  end  of 
the  belt.  In  large  belts  these  distances  should  be  a  little 
greater.  A  regular  belt-lacing  (a  strong,  pliable  strip  of 
leather)  should  be  used,  beginning  at  hole  No.  I,  and  passing 
consecutively  through  all  the  holes  as  numbered. 

In  plan  B  the  holes  are  all  made  in  a  row.  This  plan  has 
the  advantage  of  making  the  lacers  lie  parallel  with  the  mo- 
tion on  the  pulley-side.  The  lacing  is  doubled  to  find  its 
middle,  and  the  two  ends  are  passed  through  the  two  holes 
marked  4<  I  "  and  "  1^4,"  precisely  as  in  lacing  a  shoe.  The 
two  ends  are  then  passed  successively  through  the  two  series 
of  holes  in  the  order  in  which  they  are  numbered,  2,  3,  4, 
etc.,  and  2A,  $A,  4^,  etc.,  finishing  at  13  and  13 A,  which 
are  additional  holes  for  fastening  the  ends  of  the  lacer. 


Dynamos  and  Mot 

^^C^UFORH^- 
A  six-inch  belt  should  have  seven  hoTes-m  each  part,  if 

there  are  two  rows  of  holes  ;  other  widths  in  proportion  ;  with 
one  row  the  number  is  less.  Be  very  careful  to  measure  cor- 
rectly the  length  of  belt  required,  as  it  is  very  awkward  to 


FIG.  12.— METHODS  OF  LACING  A  BELT. 

The  smooth  side  of  the  leather  of  the  belt  goes  against  the  pulley.     The  dotted  lines 
represent  the  lacing  on  the  side  away  from  pulley. 

have  it  too  short  or  even  too  long  if  it  be  an  endless  belt.  If 
the  machine  has  a  belt-tightener,  measure  for  the  belt  when 
the  position  of  tightener  makes  the  belt  the  shortest,  in 
order  to  allow  for  stretch,  which  is  considerable  in  some  belts. 
Avoid  short  or  vertical  belts,  as  they  are  much  more  apt 


36  Practical  Management  of 

to  slip  than  long  or  horizontal  ones.  In  connecting  pulleys 
at  different  levels,  make  the  belt  as  nearly  horizontal  as 
possible.  The  belt  should  make  an  angle  of  at  least  45°  with 
the  vertical,  if  possible.  The  distance  between  the  centres 
of  two  belt-connected  pulleys  should  be  at  least  three  times 
the  diameter  of  the  larger  pulley,  and  it  may  well  be  four 
times  if  the  space  permits.  Make  belt  just  tight  enough  to 
avoid  slipping  without  straining  the  shaft  or  bearings.  A  new 
belt  will  not  carry  as  much  power  as  one  which  has  been 
properly  used  for  a  few  months. 

The  dynamo  or  motor  shaft  and  the  shaft  to  which  it 
is  to  be  belted  must  be  placed  exactly  parallel,  and  the 
centres  of  the  two  pulleys  must  be  exactly  opposite  each 
other  in  a  straight  line  perpendicular  to  the  shafts.  The 
machine  should  then  be  turned  slowly  by  hand  with  belt  on 
to  see  if  the  belt  tends  to  run  to  one  side  of  pulley,  which 
would  show  that  it  is  not  yet  properly  "lined  up;"  and  in 
this  case  the  machine  should  be  slightly  moved  until  the 
belt  runs  in  the  middle  of  the  pulleys  and  does  not  tend  to 
work  to  one  side.  The  pulleys  may  be  brought  into  line  by 
stretching  a  string  across  both  pulleys  parallel  with  the  belt, 
and  moving  the  machines  until  the  string  touches  both 
edges  of  both  pulleys,  if  they  have  the  same  width  of  face. 
If  not,  allow  for  difference  in  width  by  measuring  with  a 
rule  from  both  edges  of  the  narrower  pulley,  to  the  string. 
If  possible,  the  machine  and  belt  should  be  se't  and  adjusted 
so  as  to  cause  the  armature  to  move  back  and  forth  in  the 
bearings  while  running,  on  account  of  side  motion  of  belt, 
and  thus  make  the  commutator  wear  smoothly  and  distrib- 
ute the  oil  in  the  bearings, — except  in  machines  in  which 
the  pole-pieces  are  at  the  ends  of  the  armature,  as  such 
motion  might  make  it  strike.  (See  p.  142.) 

It  is  always  desirable  to  have  belts  as  pliable  as  possible  ; 
hence  the  use  of  some  good  belt-dressing  is  desirable.  Rosin 
and  other  sticky  substances  are  sometimes  used  to  increase 
the  adhesion  of  belts,  but  this  is  a  practice  which  is  only 
allowable  in  an  emergency. 

In  places  where  they  are  liable  to  catch  in  the  clothing 
or  hair  of  any  person,  belts  should  be  enclosed  by  boxing  or 
railing. 


Dynamos  and  Motors.  37 


CHAPTER  V. 
WIRING  AND  CONNECTIONS. 

Electrical  Connections. — As  already  stated,  these  should 
be  very  carefully  cleaned,  and  this  may  well  be  carried  to 
the  extent  of  rubbing  them  vigorously  with  clean  cloth  or 
chamois-skin.  Any  of  the  metal  surfaces  used  in  making 
electrical  contacts  which  are  tarnished  should  be  brightened 
with  fine  sand-paper  or  by  scraping  them  ;  but  all  sand, 
metallic  particles,  etc.,  must  be  carefully  removed  after- 
wards. Particles  of  sand  or  dirt  are  often  left  accidentally 
between  surfaces  which  should  be  in  perfect  contact. 

Wiring. — It  is  very  desirable  to  have  a  thoroughly  com- 
petent lineman  or  electrician  to  connect  a  dynamo  or  motor 
to  the  circuit,  see  that  everything  is  properly  arranged,  and 
start  the  machine  the  first  time.  The  regulations  of  the  local 
authorities,  especially  the  Fire  Underwriters,should  be  looked 
up  and  carefully  followed,  not  only  as  a  guide  to  good  con- 
struction, but  also  to  save  trouble,  expense,  and  delay  which 
might  result  from  ignoring  them. 


FIG.  13. — WIRES  CARRIED  ON  PORCELAIN. 

The  connections  should  all  be  made  in  a  substantial  and 
permanent  manner.  Good  quality  of  insulated  wire,  prefer- 
ably rubber-covered,  should  be  used,  and  should  be  properly 
arranged  and  laid. 

Temporary,  loose,  or  poorly  insulated  wires  or  connec- 
tions are  very  objectionable.  All  circuits  exposed  to  moist- 
ure should  be  supported  on  glass,  porcelain,  or  other  water- 


38  Practical  Management  of 

proof  insulators.  Circuits  of  over  250  volts,  even  where  not 
exposed  to  moisture,  should  also  be  carried  on  porcelain  or 
similar  insulators,  as  shown  in  Fig.  13,  and  out  of  reach  if 
possible. 


FIG.  14. — MOULDINGS. 

Low-voltage  circuits  of  230  volts  or  under  may  be  run  in 
wooden  moulding  or  cleats  (Fig.  14),  where  entirely  un- 
exposed  to  moisture.  Where  wires  pass  through  walls, 
floors,  over  pipes,  or  are  otherwise  liable  to  injury,  they 
should  be  protected  by  hard-rubber  tubing  or  other  equally 
good  covering.  No  wire  smaller  than  No.  8  B.  &  S.  gauge 
should  be  used  for  the  arc  current  of  10  amperes. 

The  ordinary  rule  is  that  wires  should  have  from  500  to 
1000  circular  mils  per  ampere.  The  former  figure  (500)  is 
for  small  wires,  in  cool  places;  the  latter  figure  (1000)  is  for 
wires  carrying  heavy  currents  or  high  voltage,  and  wires  in 
hot  places,  such  as  ceilings  of  kitchens,  etc.,  or  for  wires 
when  wound  in  a  coil,  in  which  case  the  rise  in  temperature 
is  much  greater.  No  wire  smaller  than  No.  16  should  ever 
be  laid  to  carry  any  current  from  a  dynamo,  no  matter  how 
small  the  current  may  be.  Smaller  wires  may  be  used  for 
primary-battery  current's. 

The  following  are  recommended  by  the  insurance  com- 
panies as  safe-carrying  capacities  for  copper  wires  when  in- 
closed in  moulding: 

Brown  &  Sharp  Brown  &  Sharp 

Gauge  No.  Amperes.  Gauge  No.  Amperes. 

oooo  175  5  45 

ooo  145  6  35 

00  120  7  30 

0  ioo          8        25 

1  95         10        20 

2  /O  12          15 

3  60         14        10 

4  50         16        5 


Dynamos  and  Motors.  39 

A  micrometer  screw  caliper  is  extremely  convenient,  and 
better  than  any  gauge  for  measuring  wires. 

It  is  wise  to  have  an  ample  margin.  .  Failure  to  allow  a 
proper  factor  of  safety  has  been  the  cause  of  most  of  the 
troubles  in  all  branches  of  electrical  work. 

In  addition  to  the  above  allowances  for  current  capacity 
or  the  ability  of  wires  to  carry  the  current  without  over- 
heating, it  is  also  necessary  to  consider  the  fall  of  potential 
or  "  drop  "  on  wires.  This  loss  is  usually  about  5  per  cent  in 
isolated  plants,  10  per  cent  in  central-station  systems,  and 
10  to  20  per  cent  in  long-distance  transmission — that  is  to 
say,  the  voltage  at  the  most  remote  point  on  the  system 
should  not  fall  below  the  voltage  at  the  dynamo  by  more 
than  these  percentages.  "  Wiring-tables  "  for  determining 
the  size  of  wire  required  in  various  cases  are  given  in  many 
electrical  books — in  fact,  there  are  several  entirely  devoted  to 
wiring,  and  the  reader  is  referred  to  them.  A  simple  rule 
derived  from  Ohm's  law,  applicable  to  all  cases,  except  with 
alternating  currents,  is  that  the  lost  voltage  or  "  drop"  on 
any  portion  of  a  circuit  is  obtained  by  multiplying  the  max- 
imum current  in  amperes  in  that  portion  by  the  resistance  of 
that  portion  of  the  circuit  in  ohms.  With  alternating  cur- 
rents an  additional  "drop"  occurs,  due  to  "  reactance," 
which,  together  with  the  ohmic  loss,  is  called  the  impedence. 

In  the  case  of  a  branching  circuit,  where  the  current  is 
not  the  same  throughout,  the  separate  parts  should  be 
treated  separately,  as  indicated  in  the  diagram. 

Dynamo 
115  Volts 

Current  = i  amp.  Current  =  10  amp. 

Resistance  going  and  Resistance  going  and, 

return  =  .25  ohm .  return  =  A  ohm. 

Drop=  .25  x  4=  1  volt.  Erop=^.4  x  10  =  4  volts. 


Voitage=  115-4-1  =11O  voltage=  115-4  =  111 


HHH        HHH 

32  c.  p.  I  lamps  32  c.  p.  (lamps 


FIG.  15. — "DROP"  ON  BRANCHING  CIRCUITS. 

Switches  and  Cut-outs. — The  bases  of  all  switches,  cut- 
outs, etc.,  should  be  of  treated  slate,  porcelain,  marble,  or 


Practical  Management  of 


other  fire-proof,  non-porous  insulating  material.     On  all  con- 
stant-potential or  multiple  arc  circuits,  double-pole  fusible 


FIG.  16. — DOUBLE-POLE  FUSIBLE  CUT-OUT,  AND  SAFETY  FUSES,  LINK 

PATTERN. 

cut-outs  should  be  put  where  each  branch  starts.  On  all  con- 
stant current  or  arc-circuits,  double-pole  cut-out  switches  (see 
page  78)  should  be  put  where  the  circuit  enters  any  buildino- 


FIG.  17. — DOUBLE-POLE  "  QUICK-BREAK  "  KNIFE-SWITCH. 

within  reach  of  firemen,  and  also  near  any  motor  or  group 
of  lamps  on  such  circuits  (Fig.  38).  All  high  voltage  circuits 
and  any  low  voltage  circuit  carrying  more  than  three  am- 
peres should  be  controlled  by  double-pole  "  quick-break  " 


Dynamos  and  Motor, 


switches  or  cut-outs,  which  will  entirely  disconnect  both 
sides  of  the  circuit.  Fig.  17  shows  a  switch  of  this  descrip- 
tion for  large  currents. 

The  exceptions  to  this  rule  are,  first,  constant-potential 
dynamos,  which  usually  have  single-pole  knife-switches,  the 
other  pole  being  permanently  connected  to  the  circuit ;  and, 
second,  constant-potential  motors,  which  generally  have  sin- 
gle-pole  switches  on  the  starting-boxes  ;  the  other  pole  being 
always  connected  to  the  circuit.  In  the  latter  case,  how- 
ever, it  is  recommended  to  put  a  double-pole  quick-break 
switch  (Fig.  17)  in  the  circuit,  also  (see  pages  63  and  79)  ;  in 
fact,  this  is  required  by  the  underwriters  in  most  cities. 

Diagrams  of  Connections  are  given  for  each  important 
case  to  show  the  connections  actually  required.  But  when  a 
machine  is  to  be  "  connected  up  "  a  competent  electrical 
engineer  should  be  consulted,  or  an  exact  diagram  should  be 
obtained  from  the  maker  of  the  machine,  as  its  connections 
may  be  peculiar,  and  cause  serious  trouble.  Diagrams  merely 
represent  the  path  of  the  current  in  the  simplest  way,  the 
important  thing  in  electrical  connections  being  to  get  these 
paths  right,  or  to  know  which  parts  or  wires  are  to  be  con- 
nected. Whether  the  path  be  straight  or  crooked,  vertical 
or  horizontal,  etc.,  is  not  of  much  consequence,  except  that 
the  crossing  of  wires  should  be  avoided  as  much  as  possible  ; 
and  where  it  occurs,  one  wire  should  be  protected  with  a 
hard  insulating-tube,  or  the  upper  wire  should  be  bent  away 
from  the  lower  one  so  that  there  can  be  no  danger  of  their 
touching  each  other.  Diagrams  of  the  three  most  impor- 
tant kinds  of  dynamo  connections  are  given  in  Figs.  18, 
19,  and  20 ;  in  fact,  nearly  all  plants  are  included  in  these 
three  fundamental  types,  which  are  described  in  the  three 
following  paragraphs.  The  other  diagrams  of  dynamo  and 
motor  connections  are  given  hereafter. 

Shunt  Dynamo,  supplying  Constant-potential  Circuit, 

is  represented  in  Fig.  18,  with  the  necessary  connections. 
The  brushes  B  and  B'  are  connected  to  the  two  conductors 
forming  the  main  circuit,  also  to  the  field-magnet  coils 
through  a  resistance-box  to  regulate  the  strength  of  current, 


42  Practical  Management  of 

and  therefore  the  magnetism  in  the  field.  A  voltmeter  is 
also  connected  to  the  two  brushes  or  main  conductors  to 
measure  the  voltage  or  electrical  pressure  between  them. 
One  of  the  main  conductors  is  connected  through  an  am- 
peremeter, which  measures  the  total  current  on  the  main  cir- 
cuit. The  lamps  or  motors  are  connected  in  parallel  between 


Resistance  Box 


FIG.  18. — SHUNT  DYNAMO,  SUPPLYING  CONSTANT-POTENTIAL  CIRCUIT, 
WITH  LAMPS  IN  PARALLEL. 

the  main  conductors  or  between  branches  from  them.  This 
represents  the  ordinary  low-tension  system  for  electric  light 
and  power  distribution  from  isolated  plants  or  central 
stations,  described  on  page  23. 

Series  Dynamo,  supplying^Constant-current  Circuit. 

— The  connections  in  this  case*  are  extremely  simple,  the 
armature,  field-coils,  amperemeter,  main  circuit,  and  lamps 
all  being  connected  in  one  series  (Fig.  19),  and  the  current 
being  kept  constant.  This  system  is  the  one  commonly  used 
for  arc-lighting,  as  described  on  page  24. 

Alternating-current  Plant. — The  proper  connections 
in  this  case  are  shown  in  Fig.  20,  in  which  the  names  of  the 
different  parts  of  the  plant  are  given,  and  which  therefore 
requires  no  explanation.  This  is  the  regular  high-tension 


Dynamos  and  Motors. 


43 


Ammeter 


FIG.    19. — SERIES    DYNAMO,    SUPPLYING  A    CONSTANT-CURRENT    CIRCUIT, 
WITH  LAMPS  IN  SERIES. 


Main  Switch 


Main  Circuit 


Switch  Board 
Transformer 
Voltmeter 


Direct 
Current 
Exciter 


HUL 


Fuse  Blocks 

Q— i 


„ 

g 

Ammeter 

FIG.  20. — ALTERNATING-CURRENT  PLANT. 


44 


Practical  Management  of 


alternating-current    system    extensively    used    for    electric- 
lighting,  as  explained  on  page  26. 

The  diagrams  of  connections  of  all  cases  of  dynamos 
coupled  together  are  given  in  Chapter  VII,  and  of  electric 
motors  in  Chapter  VIII,  where  they  are  purposely  put  to 
accompany  the  explanations  there  given. 

The  Direction  of  Rotation  of  the  various  machines  is 
sometimes  a  matter  of  doubt  or  trouble.  Almost  any 
dynamo  or  motor  is  intended  to  be  run  in  a  certain  direction, 
that  is,  it  is  called  right-handed  or  left-handed,  according  to 
whether  the  armature  revolves  right-handed,  like  the  hands 
of  a  clock,  when  looked  at  from  the  pulley  end  ;  unfortu- 
nately some  persons  reverse  this  rule,  and  consider  it  from 
the  commutator  end.  Dynamos  and  motors  are  usually 
designed  to  be  right-handed,  but  the  manufacturer  will 
make  them  left-handed  if  specially  ordered.  This  may  be 
required  because  the  other  pulley  to  which  the  machine 
is  to  be  connected  happens  to  revolve  left-handed  ;  or  it  may 
be  necessary  in  order  to  bring  the  loose  side  of  the  belt  on 
top  (page  32),  or  to  permit  the  machine  to  occupy  a  certain 
position  where  space  is  limited.  To  reverse  the  direction  of 
rotation  of  an  ordinary  shunt,  series,  or  compound  wound 
direct-current,  two-pole  dynamo  or  motor,  the  brushes  may 
simply  be  reversed  as  indicated  in  Fig.  21,  without  changing 


FIG.  21. — REVERSING  POSITION  OF  BRUSHES  TO  REVERSE  ROTATION,   ALL 
CONNECTIONS  REMAINING  THE  SAME. 

any  connection.     This  changes  the  point  of  contact  of  each 
brush   tip    180°.     If   the    machine  is  multipolar,  a   similar 


Dynamos  and  Motors.  45 

change  must  be  made,  amounting  to  90°  in  a  four-pole,  45° 
in  an  eight-pole  machine,  etc.  The  direction  of  the  current 
and  the  polarity  of  the  field-magnets  remain  the  same  as 
before  ;  all  that  is  changed  is  the  direction  of  rotation  and 
the  position  of  the  brushes.  This  applies  to  any  machine 
except  arc  dynamos  and  one  or  two  other  peculiar  ma- 
chines, which  require  to  be  run  in  a  certain  direction  to,  suit 
the  regulating  apparatus.  A  separately  excited  alternating- 
current  dynamo  can  be  reversed  in  direction  of  rotation  with- 
out changing  any  connection.  A  self-exciting  or  compound- 
wound  alternator  requires  the  brushes  that  supply  the  direct 
current  to  the  field  to  be  reversed  upon  the  commutator, 
and  their  tips  moved  through  an  angle  as  above  if  the  rota- 
tion be  reversed. 

In  any  case,  copper  brushes  (unless  they  be  gauze  brushes 
pressing  radially  upon  the  commutator)  should  point  in  the 
direction  of  rotation  ;  but  carbon  brushes,  particularly  if 
they  are  perpendicular  to  the  surface  of  the  commutator, 
allow  the  armature  to  be  revolved  in  either  direction. 

If  the  direction  of  the  current  generated  by  a  dynamo  is 
opposite  to  that  desired,  the  two  wires  leading  out  of  it 
should  exchange  places  in  the  terminals.  Or  if  this  is  not 
desired,  reverse  the  residual  magnetism  by  a  battery  or  other 
current. 

Changing  the  direction  of  the  current  by  reversing  the 
main  wires  or  otherwise  does  not  reverse  the  direction  of 
rotation  of  any  motor,  since  it  reverses  both  the  armature 
and  field.  The  way  to  reverse  the  direction  of  rotation  is  to 
reverse  either  the  armature  or  the  field  connections  alone, 
leaving  the  other  the  same  as  before. 


46  Parctical  Management  of 


CHAPTER   VI. 
DIRECTIONS  FOR  STARTING  DYNAMOS. 

General. — Make  sure  that  the  machine  is  clean  through- 
out, especially  the  commutator,  brushes,  electrical  connec- 
tions, etc.  Remove  any  metal-dust,  as  it  is  very  likely  to 
make  a  ground  or  short  circuit. 

Examine  the  entire  machine  carefully,  and  see  that  there 
are  no  screws  or  other  parts  that  are  loose  or  out  of  place. 
See  that  the  oil-cups  have  a  sufficient  supply  of  oil,  and  that 
the  passages  for  the  oil  are  clean  and  the  feed  is  at  the 
proper  rate.  In  the  case  of  self-oiling  bearings  see  that  the 
rings  or  other  means  for  carrying  the  oil  work  freely.  See 
that  the  belt  is  in  place  and  has  the  proper  tension.  If  it  is 
the  first  time  the  machine  is  started,  it  should  be  turned  a 
few  times  by  hand,  or  very  slowly,  in  order  to  see  if  the 
shaft  revolves  easily  and  the  belt  runs  in  centres  of  pulleys. 

The  brushes  should  now  be  carefully  examined  and  ad- 
justed to  make  good  contact  with  the  commutator  and  at 
the  proper  point,  the  switches  connecting  the  machine  to  the 
circuit  being  left  open.  The  machine  should  then  be  started 
with  care  and  brought  up  to  full  speed,  gradually  if  possible  ; 
and  in  any  case  the  person  who  starts  either  a  dynamo  or  a 
motor  should  closely  watch  the  machine  and  everything 
connected  with  it  and  be  ready  to  throw  it  out  of  circuit  if 
it  is  connected,  and  shut  down  and  stop  it  instantly  if  the 
least  thing  seems  to  be  wrong,  and  should  then  be  sure  to 
find  out  and  correct  the  trouble  before  starting  again. 
(See  Part  III,  "  Locating  and  Remedying  Troubles.") 

Starting  a  Dynamo. — In  the  case  of  a  dynamo  it  is 
usually  brought  up  to  speed  either  by  starting  up  a  steam- 
engine  or  by  connecting  the  dynamo  to  a  source  of  power 
already  in  motion.  The  former  should  of  course  only  be 


Dynamos  and  Motors.  47 

attempted  by  a  person  competent  to  manage  steam-engines 
and  familiar  with  the  particular  type  in  question.  This 
requires  special  knowledge  acquired  by  experience,  as  there 
are  many  points  to  appreciate  and  attend  to,  the  neglect  of 
any  of  which  might  cause  serious  trouble.  For  example,  the 
presence  of  water  in  the  cylinder  might  knock  out  the 
cylinder-head  ;  the  failure  to  set  the  feed  of  the  oil-cups 
properly  might  cause  the  piston-rod,  shaft,  or  other  part  to 
cut.  And  other  great  or  small  damage  might  be  done  by 
ignorance  or  carelessness.  The  mere  mechanical  connecting 
of  a  dynamo  to  a  source  of  power  is  usually  not  very  diffi- 
cult ;  nevertheless,  it  should  be  done  carefully  and  intel- 
ligently, even  if  it  only  requires  throwing  in  a  friction-clutch 
or  shifting  a  belt  from  a  loose  pulley.  To  put  a  belt  on  a 
pulley  in  motion  is  difficult  and  dangerous,  particularly  if 
the  belt  is  large  or  the  speed  is  high,  and  should  not  be  tried 
except  by  a  person  who  knows  just  how  to  do  it.  Even  if 
a  stick  is  used  for  this  purpose  it  is  apt  to  be  caught  and 
thrown  around  by  the  machinery,  unless  it  is  used  in  exactly 
the  right  way. 

It  has  been  customary  to  bring  dynamos  to  full  speed 
before  the  brushes  are  lowered  into  contact  with  the  com- 
mutator; but  this  is  not  necessary,  provided  the  dynamo  is 
not  allowed  to  turn  backwards,  which  sometimes  occurs  from 
carelessness  in  starting,  and  might  injure  copper  brushes  by 
causing  them  to  catch  in  the  commutator.  If  the  brushes 
are  put  in  contact  before  starting  they  can  be  more  easily 
and  perfectly  adjusted,  and  the  E.  M.  F.  will  come  up  slowly, 
so  that  any  fault  or  difficulty  will  develop  gradually  and  can 
be  corrected,  or  the  machine  can  be  stopped,  before  any 
injury  is  done  to  it  or  to  the  system.  In  fact,  if  the  machine 
is  working  alone  on  a  system,  and  is  absolutely  free  from  any 
danger  of  short-circuiting  any  other  machine  or  storage 
battery  on  the  same  circuit,  it  may  be  started  while  con- 
nected to  the  circuit,  but  not  otherwise  (see  next  chapter). 
If  there  are  a  large  number  of  lamps  connected  to  the  cir- 
cuit, the  field  magnetism  and  voltage  might  not  be  able  to 
"  build  up  "  until  the  line  is  disconnected  an  instant  (see 
Dynamo  Fails  to  Generate,  Cause  3,  page  157). 


48  Practical  Management  of 

If  one  dynamo  is  to  be  connected  to  another  or  to  a 
circuit  having  other  dynamos  or  a  storage  battery  working 
upon  it,  the  greatest  care  should  be  taken.  This  coupling 
together  of  dynamos  can  be  done  perfectly,  however,  if 
the  correct  method  is  followed,  but  is  likely  to  cause  serious 
trouble  if  any  mistake  is  made. 


Dynamos  and  Motors.  49 


CHAPTER  VII. 
SWITCHING  DYNAMOS  INTO  CIRCUIT. 

TWO  or  more  machines  are  often  connected  to  a  com- 
mon circuit.  This  is  especially  the  case  in  electric-lighting, 
where  the  number  of  lamps  required  to  be  fed  varies 
so  much  that  one  dynamo  may  be  sufficient  for  certain 
hours,  but  two,  three,  or  more  machines  may  be  required 
at  other  times.  The  various  ways  in  which  this  is  done 
depending  upon  the  character  of  the  machines  and  of  the 
circuit  and  the  precautions  necessary  in  each  case,  make 
this  a  most  important  and  interesting  subject,  which  requires 
careful  consideration. 

Dynamos  may  be  connected  together  either  in  parallel 
(multiple  arc)  or  in  series. 

Dynamos  in  Parallel. — In  this  case  the  -f-  terminals  are 
connected  together  or  to  the  same  line  and  the  —  terminals 
are  connected  together  or  to  the  other  line.  The  currents 
(i.e.,  amperes)  of  the  machines  are  thereby  added,  but  the 
E.  M.  F.  (volts)  are  not  increased.  The  chief  condition  for 
the  running  of  dynamos  in  parallel  is  that  their  voltages 
shall  be  equal,  but  their  current  capacities  may  be  different. 
For  example :  A  dynamo  producing  10  amperes  may  be 
connected  to  another  generating  100  amperes,  provided  the 
voltages  agree.  Parallel  working,  is,  therefore  suited  to  con- 
stant potential  circuits.  A  dynamo  to  be  connected  in 
parallel  with  others  or  with  a  storage  battery  must  first  be 
brought  up  to  its  proper  speed,  E.  M.  F.,  and  other  working 
conditions,  otherwise  it  will  short-circuit  the  system,  and 
probably  burn  out  its  armature.  Its  field  magnetism  must 
therefore  be  at  full  strength  owing  to  the  fact  that  it 
generates  no  E.  M.  F.  with  no  field  magnetism.  Hence  it  is 
well  to  find  whether  the  pole-pieces  are  strongly  magnetized 
by  testing  them  with  a  piece  of  iron,  and  to  make  sure  of 


5° 


Practical  Management  of 


the  proper  working  of  the  machine  in  all  other  respects 
before  connecting  the  armature  to  the  circuit.  It  is  a 
common  accident  for  the  field-circuit  to  be  open  at  some 
point,  and  thus  cause  very  serious  results.  In  fact,  a  dynamo 
should  not  be  connected  to  a  circuit  in  parallel  with  others 
until  its  voltage  has  been  tested  and  found  to  be  equal  to 
or  slightly  (not  over  I  or  2  per  cent)  greater  than  that  of 
the  circuit.  If  the  voltage  of  the  dynamo  is  less  than  that 
of  the  circuit  the  current  will  flow  back  into  the  dynamo 
and  cause  it  to  be  run  as  a  motor.  The  direction  of  rotation 
is  the  same,  however,  if  it  is  shunt-wound,  and  no  great 
harm  results  from  a  slight  difference  of  potential.  But  a 
compound-wound  machine  requires  more  careful  handling 
(see  page  53). 

Dynamos  in  Parallel  are  therefore  ahvays  SI mnt -wound 
(or  Compound-wound). — The  test  for  equal  voltages  may  be 
made  by  first  measuring  the  E.  M.  F.  of  the  circuit  and  then 
of  the  machine  by  one  voltmeter ;  or  voltmeters  connected 


Field 

Regulator  Amir-Jeter  I     Field  Regulator  Amr 

.Voltmeter/ 


FIG.  22. — SHUNT  DYNAMOS  IN  PARALLEL. 

to  each  may  be  compared  (Fig.  22).  Another  method  is  to 
connect  the  dynamo  to  the  circuit  through  a  high  resistance 
and  a  galvanometer,  and  when  the  latter  indicates  no  cur- 
rent it  shows  that  the  voltage  of  the  dynamo  is  equal  to 
that  of  the  circuit.  A  rougher  and  simpler  way  to  do  this 
is  to  raise  the  voltage]  of  the  dynamo  until  its  "  pilot-lamp," 


Dynamos  and  Motors.  5 1 

or  other  lamp  fed  by  it,  is  fully  as  bright  as  the  lamps  on 
the  circuit,  and  then  connect  the  dynamo  to  the  circuit. 
Of  course  the  lamps  compared  should  be  intended  for  the 
same  voltage  and  in  normal  condition.  Be  sure  to  connect 
the  positive  terminal  of  the  dynamo  to  the  positive  wire, 
and  the  negative  terminal  to  the  negative  wire  (Fig.  22) ; 
otherwise  there  will  be  a  very  bad  short-circuit. 

When  the  dynamo  is  first  connected  in  this  way  it  should 
only  supply  a  small  amount  of  current  to  the  circuit  (as 
indicated  by  its  ammeter),  and  its  voltage  should  then  be 
gradually  raised  until  it  generates  its  proper  share  of  the 
total  current ;  otherwise  it  will  cause  a  sudden  jump  in  the 
brightness  of  the  lamps  on  the  circuit. 

Series-wound  Dynamos  in  Parallel  not  Used. — If  the 
machine  is  series-wound,  the  back  current  just  described 
would  cause  a  reversal  of  field  magnetism  and  a  short-cir- 
cuit of  double  voltage,  which  is  fatal.  In  fact,  series  dyna- 
mos in  parallel  are  in  very  unstable  equilibrium,  because  if 


Main 


Main, 


FIG.  23.— SERIES  DYNAMOS  IN  PARALLEL,  ARRANGED  TO  BALANCE. 

either  tends  to  generate  too  little  current,  that  weakens  its 
own  field,  which  is  in  series,  and  thus  still  further  reduces 
its  current,  and  probably  reverses  the  machine.  This 
arrangement  is  therefore  not  used.  One  way  in  which  this 
difficulty  might  be  overcome,  is  by  causing  each  to  excite 
the  other's  field-magnet,  as  shown  in  Fig.  23,  so  that  if  one 
generates  too  much  current,  it  strengthens  the  field  of  the 
other,  and  thus  counteracts  its  own  excess  of  power. 


52  Practical  Management  of 

Or  both  fields  may  be  so  connected  as  to  be  excited  by 
one  machine,  or,  better,  by  both  machines  jointly,  which 
is  accomplished  by  connecting  together  the  two  -\-  brushes 
and  the  two  —  brushes  respectively,  by  the  line  and  by  what 
is  called  an  "  equalizer  "  (Fig.  24).  By  this  means  the  electri- 


Main 


FIG.  24. — SERIES  DTNAMOS  IN  PARALLEL,  WITH  FIELD  CURRENTS 
"  EQUALIZED." 

cal  pressure  at  the  terminals  of  the  two  armatures  is  made 
the  same,  and  the  currents  in  the  two  fields  are  also  made 
equal.  Series  machines  are  not  often  run  in  parallel,  but 
the  principles  just  explained  help  the  understanding  of  the 
next  case,  which  is  extremely  important. 

Compound  Dynamos  in  Parallel. — Since  the  field-magnets 
of  these  machines  are  wound  with  series  as  well  as  shunt 
coils,  the  coupling  of  them  is  a  combination  of  the  cases  of 
the  shunt  and  the  series  wound  machines  just  described. 

Fig.  25  represents  in  simplest  outline  two  compound  ma- 
chines in  parallel. 

Assume  that  one  machine  is  already  running,  that  switches 
F1  in  the  shunt  circuit  and  S1  in  the  main  circuit  are  closed, 
and  that  armature  No.  I  is  generating  its  full  current,  and 
feeding  the  lamps  on  the  main  circuit,  the  shunt  and  series 
field-coils  of  the  machine  carrying  their  proper  current. 
Now  to  throw  on  the  other  dynamo,  its  armature  (No.  2)  is 
brought  up  to  normal  speed,  switch  F2  is  closed,  which 
excites  its  shunt-coil.  Switch  E,  on  the  " equalizer"  is  then 
closed,  which  excites  its  series  coil  with  part  of  the  main 


OF   THK 

UNIVERSITY 


Dynamos 


53 


current  from  No.  I.  The  voltage  of  the  machine  to  be  con- 
nected (No.  2)  should  then  be  compared  with  and  made 
about  one  per  cent  higher  than  that  of  the  circuit,  and  then 
it  may  be  thrown  in  by  closing  the  main  switch  S2,  as  de- 
scribed for  shunt  machines  on  page  50.  The  machine  should 


Switch  or  Rheostat 


FIG.  25.— OUTLINE  OF  CONNECTIONS,  COMPOUND  DYNAMOS  IN  PARALLEL, 
WITH  EQUALIZER  BAR. 

only  generate  a  small  current  at  first,  but  it  may  then  be  regu- 
lated by  its  rheostat  to  carry  its  share  of  the  load.  The 
"  equalizer"  should  be  closed  before  the  main  switch  and 
before  comparing  the  voltages,  otherwise  the  machine  will 
take  too  much  load  at  first.  Greater  care  and  closer  agree- 
ment in  voltage  is  required  with  compound  than  with  plain 
shunt  dynamos  both  in  coupling  and  in  running. 

In  disconnecting  a  machine  the  same  steps  are  taken, 
only  in  exactly  the  reverse  order.  More  than  two  com- 
pound machines  may  be  run  in  parallel  in  this  way  by  con- 
necting them  in  a  precisely  similar  manner. 

Compounding  is  most  extensively  used  in  the  large 
modern  types  of  dynamos,  which  are  nearly  all  multipolar, 
four  poles  being  the  most  common.  In  these  (Fig.  26) 
there  are  as  many  spools  as  fields,  and  as  each  contains  both 
series  and  shunt  coils  the  connections  become  complicated. 
Fig.  27  represents  the  connections  of  a  standard  four-pole 
compounded  generator  and  of  a  shunt-wound  generator.  If 
the  four  coils  are  taken  as  one,  it  will  be  seen  that  they  are 
the  same  as  Figs.  25  and  18,  respectively. 

Compound  dynamos  of  different  size  or  current  capacity 


54 


Practical  Management  of 


may  also  be  coupled  as  described,  provided  of  course  their 
voltages  are  equal,  and  provided  also  that  the  resistances  of 


the  series  field-coils  are  inversely  proportional  to  the  cur- 
rent capacities  of  the  several  machines  ;  that  is,  if  a  dynamo 


Dynamos  and  Motors. 


55 


produces  twice  as  much  current,  its  series-coil  should  have 
half  the  resistance.  It  is  further  necessary  that  the  two 
machines  should  agree  in  their  action,  so  that  a  given  in- 


00  Co 


crease  in  load  will  produce  the  same  effect  upon  their 
voltages.  If  they  are  not  in  agreement,  they  may  be 
adjusted  by  slightly  increasing  the  resistance  of  the  series- 


56  Practical  Management  of 

coil  of  the  machine,  which  tends  to  take  too  large  a  share  of 
the  load.  This  may  be  done  by  simply  interposing  a  few 
extra  feet  of  conductor  of  the  same  current  capacity  as  the 
series-coil  between  the  latter  and  the  main  conductor  or 
'bus  bar.  The  shunts  which  are  almost  always  used  to  ad- 
just the  effect  of  the  series-coils  in  compound  dynamos 
(shown  at  Z  in  machine  No.  I,  Fig.  25  ;  and  at  upper  left- 
hand  corner  of  compound  dynamo  in  Fig.  27)  operate 
properly  in  the  case  of  machines  working  singly,  but  are 
worthless  for  machines  in  parallel.  The  resistances  of  the 
series-coils  themselves  must  be  adjusted  as  explained  above, 
when  two  or  more  compound  machines  are  run  in  parallel. 
The  use  of  iron  for  the  shunt  makes  the  compounding  effect 
in  the  dynamo  more  uniform,  because  its  resistance  rising  as 
the  current  through  it  increases,  throws  a  greater  portion  of 
the  current  through  the  series-coils  at  full  load,  and  compen- 
sates for  the  fact  that  the  field-magnetism,  and  consequently 
voltage,  does  not  increase  proportionately  with  the  increasing 
load  current. 

The  switch  E  is  often  left  closed  all  the  time  ;  in  fact  a 
permanent  "  equalizing  "  connection  may  be  made  between 
the  corresponding  brushes  of  two  or  more  machines.  This 
has  the  effect  of  "  compounding"  the  dynamos  collectively 
instead  of  individually.  For  example,  when  only  one  dyn- 
amo is  working,  its  current  divides  among  the  series-coils 
of  all,  and  these  coils  will  not  be  highly  excited  ;  when, 
however,  all  the  dynamos  are  working,  the  whole  current  of 
each  will  pass  through  its  series-coil.  Thus  the  greatest 
field  strength,  and  therefore  voltage,  is  produced  when  most 
needed,  at  the  full  load  of  all  the  machines.  The  equalizing 
conductor  should  be  able  to  carry  at  least  half  the  full  cur- 
rent of  one  dynamo  in  the  case  of  two  machines,  and  of  still 
greater  capacity  when  there  are  more  machines.  Trouble 
has  often  been  caused  by  the  use  of  too  small  equalizing 
conductors.  This  method  of  running  compound  dynamos 
in  parallel,  without  opening  the  equalizing  connection,  is 
important,  because  it  makes  the  effect  of  the  series-coil 
proportional  to  the  total  load,  instead  of  the  load  on  each 
machine.  This  is  particularly  desirable  in  central  stations, 
or  where  dynamos  are  "  overcompounded."  Shunt-wound 


Dynamos  and  Motors.  5  7 

dynamos  run  in  parallel  tend  to  steady  each  other,  for  if 
one  happens  to  run  too  fast  it  has  to  do  more  work,  which 
opposes  the  increase  of  speed,  and  it  also  takes  part  of  the 
load  off  the  other  machines,  which  makes  them  run  faster, 
thus  producing  equality.  This  mutual  regulation  will  take 
care  of  any  slight  difference  between  machines,  such  as 
that  caused  by  the  slip  of  the  belt,  or  even  small  differences 
in  the  governing  action  of  the  different  engines  that  may  be 
driving  them.  Compound-wound  dynamos  have  very  much 
less  mutual  regulation,  owing  to  the  effect  of  the  series-coil, 
and  it  is  necessary  that  their  speeds,  voltages,  etc.,  should 
agree  much  more  exactly  than  with  simple  shunt  machines. 
It  is  not  uncommon  for  them  to  work  badly  together, 
owing  to  carelessness  or  imperfect  agreement  between  them, 
but  with  proper  care  and  good  apparatus  they  run  well  in 
parallel. 

Alternators  in  Parallel. — Since  the  alternating  current 
consists  of  waves,  it  is  necessary,  in  order  to  properly  con- 
nect alternators  together,  that  they  should  agree,  not  only 
in  voltage,  but  also  in  two  other  respects :  first,  in  frequency, 
or  the  number  of  waves  produced  per  second ;  and,  second, 
in  phase,  that  is,  their  current  waves  should  be  at  corre- 
sponding points  at  the  same  instant.  The  case  is  precisely 
similar  to  that  of  two  persons  walking  together  :  they  should 
not  only  have  the  same  speed  and  length  of  step,  but  they 
should  also  be  /;/  step.  If  an  alternator  is  thrown  into  cir- 
cuit with  others  when  not  exactly  in  phase,  it  will  cause 
severe  fluctuations  in  the  lamps. 

Even  the  highest  authorities  do  not  agree  in  regard  to 
the  best  conditions  for  parallel  running  of  alternators,  but 
it  is  certainly  a  fact  that  there  is  quite  a  strong  tendency  for 
alternators  working  in  parallel  to  remain  in  phase  after  they 
have  once  been  brought  exactly  into  unison,  for  the  same 
reason  that  alternating-current  motors  tend  to  run  syn- 
chronously with  the  generator,  the  action  being  similar  to 
that  of  two  cog-wheels. 

In  a  number  of  European  stations  alternators  are  regu- 
larly and  successfully  operated  in  parallel,  but  in  America 
this  practice  is  not  common.  This  difference  is  probably 
due  chiefly  to  the  fact  that  the  frequency  usual  in  this  coun- 
try is  higher  than  in  Europe,  which  necessitates  an  exceed- 


58  Practical  Management  of 

ingly  close  agreement  in  order  that  machines  may  work  well 
together.  For  example,  an  alternator  with  16  poles  and 
1000  revolutions  per  minute  would  be  entirely  thrown  out 
of  phase  if  it  differed  T*F  of  a  revolution  from  the  other 
machine.  Nevertheless,  this  running  in  parallel  can  be  and 
is  done  successfully,  provided  the  engines  as  well  as  dynamos 
are  properly  adjusted  to  each  other.  A  sudden  change  in 
the  number  of  lamps  in  circuit  might  produce  a  different 
effect  on  the  dynamos  or  engines,  and  would  throw  them 
out  of  synchronism.  For  example,  the  governor  of  one 
engine  might  act  more  slowly  than  that  of  the  other,  and 
cause  the  former  engine  to  fall  behind.  Other  similar  differ- 
ences in  action  have  made  it  difficult  or  impossible  to  run 
alternators  in  parallel  in  many  cases  but  if  the  conditions 
are  favorable  there  is  no  trouble,  and  the  actual  operation  is 
as  follows : 

To  throw  an  alternator  into  circuit  with  others,  bring  its 
speed  up  to  the  proper  point,  regulate  the  field-exciting 
current  to  make  the  voltage  of  the  machine  equal  to  that  of 
the  circuit.  The  phase  may  then  be  determined  by  connect- 
ing two  lamps  in  series  to  the  secondary  circuits  of  two 
transformers  at  the  same  time,  the  primary  circuits  being 
fed  respectively  by  the  machine  to  be  switched  in  and  by 
the  others,  or  the  main  circuit. 


FIG.  28. — METHOD  OF  BRINGING  ALTERNATORS  INTO  SYNCHRONISM. 

The  secondaries  of,  say,  50  volts  each  should   be   con- 
nected in  series  with  each  other  and  to  two   5ovolt  lamps. 


Dynamos  and  Motors. 


59 


When  the  phases  of  the  currents  of  the  two  machines  are 
opposed  the  lamps  are  dim,  and  vice  versa.  If  the  lamps 
flicker  badly  the  phase  is  not  right ;  but  if  the  lamps  are 
steady  at  full  brightness,  the  machine  is  in  phase,  and  it  may 
be  connected  without  disturbing  the  circuit  by  closing  its 
main  switch. 

If  dynamos  are  rigidly  connected  to  each  other  or  to  the 
engine,  so  that  they  necessarily  run  exactly  together,  there 
is  no  need  of  bringing  them  into  step  each  time,  but  they 
should  be  adjusted  to  the  same  phase  in  the  first  place. 

Dynamos  in  Series. — This  arrangement  is  less  common 
than  parallel  working,  and  does  not  usually  operate  so  well, 
except  with  series-wound  machines  on  arc  circuits,  which  are 
very  successful.  (See  Part  IV.)  The  conditions  are  exactly 
opposite  to  those  in  the  preceding  group  —  dynamos  in 
parallel. 

To  connect  machines  in  series,  the  positive  terminal  of 
one  must  of  course  be  connected  to  the  negative  terminal 
of  the  next,  and  so  on.  If  dynamos  are  in  series,  each  of 
them  must  have  a  current  capacity  equal  to  the  maximum 
current  on  the  circuit,  but  they  may  differ  to  any  extent  in 
E.  M.  F.  The  voltages  of  machines  in  series  are  added  to- 
gether, and  therefore  danger  to  persons,  insulation,  etc.,  is 
increased  in  proportion. 

Series-wound  Dynamos  in  Series  are  connected  in  the 
simple  way  represented  in  Fig.  29,  but,  usually,  machines 

connected  in  series  are  for  arc-  vx       ^ ^       x/ 

lighting, — for  example,  when 
two  dynamos,  each  of  40  lights 
capacity,  are  run  on  one  circuit 
of  80  lamps,  in  which  case  the 
dynamos  usually  have  some 
form  of  regulator.  These  regu- 
lators do  not  usually  work  well 
together,  because  they  are  apt 
to  "  seesaw  "  with  each  other. 
This  difficulty  may  be  over-  FIG.  29. -SERIES- WOUND  DYNAMOS 

•  ,11  ,  •  i  IN   oERIKS. 

come  either  by  connecting  the 

regulators  so  that  they  work  together,  or  by  setting  one 


6o 


Practical  Management  of 


regulator  to  give  full  E.  M.  F.  and  let  the  other  alone  con- 
trol the  current.  This  latter  plan  can  only  be  followed 
when  the  variation  in  load  does  not  exceed  the  power  of 


FIG.  30. — SHUNT  DYNAMOS  IN  SERIES.     FIELDS  JOINED  AND  FED  BY  BOTH 

ARMATURES. 

one  machine.  Constant-current  or  "  series  "  dynamos  having 
regulators  with  little  inertia  in  the  moving  parts  or  ten- 
dency to  "  overshoot,"  such  as  the  Brush  machine,  can  be 
run  in  series  without  much  trouble. 


FIG.  31. — COMPOUND  DYNAMOS  IN  SERIES,  SHUNT  COILS  OF  EACH 
EXCITED  BY  ARMATURE  OF  THE  OTHER. 

Shunt   or    Compound  Dynamos    in   Series    may   be   run 
well,  provided  the  shunt  field-coils  are  connected  together  to 


Dynamos  and  Motors.  61 

form  one  shunt  across  both  machines,  as  indicated  in  Fig. 
30.  If  the  machine  is  compound,  the  series-coils  must  be 
connected  in  series  in  the  main  circuit.  Or  each  shunt  field 
may  be  connected  so  that  it  is  fed  only  by  the  armature  of 
the  other  machine  (Fig.  31).  Or  both  the  shunt-coils  may  be 
connected  so  as  to  be  fed  by  one  armature,  the  series-coils 
being  in  the  main  circuit,  as  before, 

Alternators  in  Series. — The  synchronizing  tendency 
which  makes  it  possible  under  certain  circumstances  "to  run 
alternators  in  parallel  (page  57)  causes  them  to  get  out  of 
step  and  become  opposed  to  each  other  when  it  is  attempted 
to  run  them  in  series.  It  is  therefore  impracticable  to  run 
them  in  series  unless  their  shafts  are  rigidly  connected  to- 
gether so  they  must  run  exactly  in  phase,  and  add  their 
waves  of  current,  instead  of  counteracting  each  other.  This 
is  a  case  that  rarely  arises  in  practice. 

Dynamos  on  the  Three-wire  System  (Direct  Cur- 
rent).— In  the  ordinary  three-wire  system  for  incandescent- 
lighting,  as  represented  in  Fig.  32,  no  particular  precautions 
are  required  in  starting  or  connecting  dynamos.  As  a  matter 
of  fact,  the  two  dynamos  are  almost  independent  of  each 
other,  and  work  on  practically  separate  circuits.  Dynamo  I 
feeds  the  circuit  formed  by  the  mains  marked  -f-  and  Nt  and 
dynamo  2  feeds  the  circuit  formed  by  mains  ^Vand — ,  The 
"neutral"  wire  N  merely  acts  as  a  common  conductor  for 
both  circuits.  There  is,  however,  a  tendency  for  one  of  the 
dynamos  to  be  reversed  by  the  other  in  starting  up,  shutting 
down,  or  in  case  of  a  bad  short  circuit.  This  may  be 
avoided  by  exciting  all  the  field  coils  from  one  dynamo  or 
"  side  "  of  the  system.  (See  page  52.)  This  and  other  difficul- 
ties on  three-wire  circuits  are  treated  on  page  154.  The 
E.  M.  F  on  each  circuit  should  be  kept  constant  at  the  pre- 
cribed  voltage,  and  the  current  on  the  two  circuits  or  "  sides  " 
of  the  system  should  be  kept  as  nearly  equal  as  possible  by 
distributing  the  lamps  equally  between  them.  Any  difference 
in  current  either  way  is  carried  by  N.  One  dynamo  may  be 
run  alone  on  one  side  of  the  system,  and  the  only  effect  of 
throwing  on  the  other  dynamo  is  to  reduce  the  "  drop  "  or  fall 
of  potential  on  the  wire  N,  In  fact,  if  the  load  is  equal  on 


62 


Practical  Management  of 


both  sides  there  is  practically  no  current  or  drop  in  N.  If 
additional  dynamos  are  put  on  the  circuit  in  parallel — for 
example,  two  in  parallel  on  each  side  of  the  system,  making 
four  dynamos  in  all — the  machines  on  each  side  are  managed 
simply  as  dynamos  in  parallel,  as  previously  described,  and 
they  may  be  thrown  in  singly  or  in  pairs  (i.e.,  one  on  each 


ill 


no 


220 

Volts 


FIG.  32.— THREE-WIRE  SYSTEM. 

"  side  ").     This  applies   not  only  to  the  first  dynamos,  but 
also  to  those  added  in  parallel  afterward. 

When  only  one  dynamo  is  running,  the  lamps,  etc.,  on 
both  sides  can  be  kept  going  by  converting  the  system  into 
a  two-wire  system  temporarily  by  joining  the  two  outside 
wires  together  by  a  "  breakdown  switch."  But  if  there  are 
chemical  meters  on  the  circuit  that  is  thus  reversed,  they 
will  be  run  backward.  Besides,  the  middle  wire  has  to  carry 
as  much  current  as  the  two  outside  wires  combined,  which 
might  be  very  excessive ;  therefore  this  arrangement  should 
not  be  employed  with  heavy  loads. 


Dynamos  and  Motors.  63 


CHAPTER  VIII. 
"KINDS  OF  MOTORS  AND  METHODS  OF  STARTING. 

THE  general  instructions  relating  to  adjustment  of 
brushes,  screws,  belt,  oil-cups,  etc.,  given  in  the  chapter  on 
starting  dynamos,  should  be  carefully  followed  preparatory 
to  starting  a  motor. 

The  actual  starting  of  a  motor  is  usually  a  simple  matter, 
since  it  consists  merely  in  operating  a  switch,  but  in  each 
case  there  are  one  or  more  important  points  to  consider. 

For  Constant-potential  Circuit,  Shunt-Wound  Motor. — 
A  motor,  to  run  at  constant  speed  on  a  constant-potential  cir- 
cuit (a  iio-volt  incandescent-lighting  circuit,  for  example), 
is  usually  plain  shunt-wound.  This  is  the  commonest  form 
of  stationary  motor.  The  field-coils  are  wound  with  the 
right  size  of  wire  to  have  sufficient  resistance,  so  that  they 
will  take  the  proper  magnetizing  current,  as  in  the  case  of  a 
shunt  dynamo,  and,  since  the  potential  is  constant,  the  field 
strength  is  constant.  Shunt-coils  should  be  rewound  or  ex- 
changed for  those  having  the  proper  size  and  resistance  of 
wire,  if  the  potential  is  more  than  10  per  cent  higher,  or 
20  per  cent  lower  than  that  for  which  they  are  intended. 

In  starting  shunt  motors,  throwing  the  field  into  circuit 
is  simple.  The  difficulty  is  in  taking  care  of  the  current  in 
the  armature,  because  the  resistance  of  the  armature  is  very 
low,  in  order  to  get  high  efficiency  and  constancy  of  speed,  and 
the  rush  of  current  through  it  in  starting  might  be  twenty 
or  more  times  the  normal  number  of  amperes.  To  prevent 
this  excessive  current,  motors  are  started  on  constant-po- 
tential circuits  through  a  rheostat  or  "  starting-box  "  contain- 
ing resistance-coils  (Fig.  34). 

The  main  wires  are  connected  through  a  branch  cut-out 
(with  safety-fuses),  and  preferably  also  a  double-pole  quick- 
break  switch  Q,  to  the  motor  and  box,  as  indicated  in  Fig. 


64 


Practical  Management  of 

Cttt-ouf 


FIG.  33.— SHUNT  MOTOR  ON  CONSTANT-POTENTIAL  CIRCUIT 


FIG.  34.— RESISTANCE-COILS, 


Dynamos  and  Motors.  65 

33.  When  the  switch  Q  is  closed  and  the  arm  Sis  turned  to 
the  right,  the  field  circuit  is  closed  through  the  contact  strip 
F,  and  the  armature  circuit  is  closed  through  the  resistance- 
coils  a,  a,  a,  which  prevent  the  rush  of  current  referred  to. 
The  motor  then  starts,  and  as  its  speed  rises  it  generates  a 
counter  E.  M.  F.,  so  that  the  arm  S  can  be  turned  further 
until  all  the  resistance-coils  a,  a,  a  are  cut  out,  and  the  mo- 
tor is  directly  connected  to  the  circuit  and  running  at  full 
speed.  The  arm  S  should  be  turned  slowly  enough  to  allow 
the  speed  and  counter  E.  M.  F.  to  come  up  as  the  resistances 
a,  a,  a  are  cut  out.  The  arm  5"  should  positively  close  the 
field  circuit  first,  so  that  the  magnetism  reaches  its  full 
strength  (which  takes  several  seconds)  before  the  armature 
is  connected. 

The  object  of  the  resistance  f  is  to  gradually  decrease 
the  current  and  thereby  reduce  the  spark,  which  occurs 
when  the  field  circuit  is  opened.  But  this  resistance  is  not 
essential,  and  some  boxes  have  a  number  of  strips  which 
merely  subdivide  the  spark,  and  others  have  no  connection 
at  all  between  the  field-coils  and  the  starting  or  regulating 
box,  the  circuit  being  led  directly  from  the  switch  Q  to  the 
field,  the  armature  alone  being  connected  through  the 
resistance-box.  The  coils  a,  a,  a  are  made  of  comparatively 
fine  wire,  which  can  only  carry  the  current  for  a  few  seconds 
in  a  "  starting-box  ;  "  but  if  the  wire  is  large  enough  to  carry 
the  full  current  continuously,  it  is  called  a  "regulator,"  be- 
cause the  arm  5  may  be  left  so  that  some  of  the  resistances 
a,  a,  a  remain  in  circuit,  and  they  will  have  the  effect  of 
reducing  the  speed  of  the  motor,  which  is  often  very  desirable. 

In  some  cases  where  a  circuit  is  used  exclusively  for  a 
single  motor,  the  speed  is  regulated  without  heavy  resist- 
ances by  varying  the  E.  M.  F.  of  the  dynamo  which  supplies 
the  circuit.  The  dynamo  regulator  is  then  placed  near  the 
motor.  The  advantage  is  that  the  regulator  does  not  have 
to  control  a  heavy  current,  but  a  special  circuit  of  unvaried 
pressure  has  to  be  provided  to  keep  the  field  of  the  motor 
constant. 

For  Constant-potential  Circuit,  Series-wound  Motor. — 
The  ordinary  electric  railway  motor  on  the  5OO-volt  trolley 


66  Practical  Management  of 

system  is  the  chief  example  of  this  class  (Fig.  35).  Motors 
for  electric  elevators  and  hoists  are  either  of  this  kind  or  the 
previous  one.  A  rush  of  current  tends  to  occur  when  this 


FIG.  35. — STANDARD  STREET-CAR  MOTOR,  WITH  ONE  SET  OF  GEARS  OR 
"SINGLE  REDUCTION"  OF  SPEED. 

type  of  motor  is  started,  similar  to  that  in  the  case  just  de- 
scribed ;  but  it  is  somewhat  less,  because  the  field-coils  are 
in  series,  and  their  resistance  and  self-induction  reduce  the 
excess. 

The  connections  as  indicated  in  Fig.  36  are  very  simple, 
the  armature,  field-coils  F F,  and  rheostat  all  being  in  series 
and  carrying  the  same  current. 

The  series-wound  motor  on  a  constant-potential  circuit 
does  not  have  a  constant  field  strength,  and  does  not  tend 
to  run  at  constant  speed,  like  a  shunt  motor.  In  fact  it  may 
"  race  "  and  tear  itself  apart  if  the  load  is  taken  off  entirely ; 
it  is  therefore  only  suited  to  railway,  pump,  fan,  or  other 
work  where  variable  speed  is  desired,  or  where  there  is  no 


Dynamos  and  Motors.  67 

danger  of  the  load  being  removed  or  a  belt  slipping  off. 
They  are  also  used  where  the  potential  is  subject  to  sudden 
and  large  drops,  as  on  the  ends  of  long  trolley  circuits, 
because  in  such  a  case  a  shunt  motor  becomes  momentarily 
a  generator  and  sparks  very  badly. 


FIG.  36. — SERIES-WOUND   MOTOR  AND  CONTROLLER  ON  CONSTANT-POTEN- 
TIAL CIRCUIT. 

The  fields  of  series  motors  are  sometimes  "  overwound  ;" 
that  is,  so  wound  that  they  will  have  their  full  strength  with 
even  one-half  or  one-third  of  the  normal  current.  The  object 
of  this  is  to  secure  constant  speed  with  varying  load,  as  with 
a  shunt  motor.  Also  in  railway  motors  to  enable  them  to 
run  at  high  economy  when  drawing  small  currents  and  to 
prevent  sparking  at  heavy  load. 

In  multipolar  motors  having  more  than  two  field-coils 
the  coils  are  all  connected  together,  and  are  equivalent  to 
the  single  pairs  of  coils  shown  in  the  several  diagrams.  Be- 
ing separated,  however,  it  is  sometimes  necessary  to  trace 
out  the  connections.  Fig.  37  represents  all  the  connections 
of  a  four-pole  motor,  shunt-wound  and  series-wound. 

For  Constant-potential  Circuit,  Differentially-wound 
Motor. — This  is  a  shunt-wound  motor  with  the  addition  of  a 
coil  of  large  wire  on  the  field  connected  in  series  with  the 
armature  in  such  a  way  as  to  oppose  the  magnetizing  effect 


6g  Practical  Management  of 

of  the  shunt-winding,  weaken  the  field,  and  thus  cause  the 
motor  to  speed  up  when  the  load  is  increased,  as  an  offset  to 
the  slowing-down  effect  of  load. 

It  was  formerly  much  used  to  obtain  very  constant  speed, 
but  it  has  been  found  that  a  plain  shunt  motor  is  sufficiently 

CONNECTIONS  FOR  SHUNT  WOUND  MOTORS.  CONNECTIONS  FOR  SERIES  WOUND  MOTORS. 


O,  OUTSIDE  TERMINAL  OF  COIL.      |,  INSIDE  TERMINAL  OF  COIL. 

FIG.  37. 

constant  for  almost  all  cases.  The  differential  motor  has 
the  great  disadvantage  that,  if  overloaded,  the  current  in 
the  opposing  (series)  field-coil  becomes  so  great  as  to  kill  the 
field-magnetism,  and  instead  of  increasing  or  keeping  up  its 
speed,  the  armature  slows  down  or  stops,  and  is  liable  to 
burn  out ;  whereas  a  plain  shunt  motor  can  increase  its 
power  greatly  for  a  minute  or  so  when  overloaded,  and  will 
probably  throw  off  the  belt  or  carry  the  load  until  the  latter 
decreases  to  the  normal  amount. 

For  Constant-current   Circuit,  Series-wound  Motor.— 
The  commonest  example  is  a  series-wound  motor  on  the 


Dynamos  and  Motors.  69 

arc  circuit.  The  connections  are  shown  in  Fig.  38.  The 
switch  i  is  to  entirely  disconnect  the  circuit  from  the  build- 
ing in  case  of  fire  or  other  emergency.  By  simply  turn- 
ing the  other  switch  2  the  motor  is  started  "or  stopped  ;  and 
since  the  current  is  constant,  the  motor  may  be  overloaded 


FIG.  38. — SERIES  MOTOR  ON  CONSTANT-CURRENT  CIRCUIT. 

or   held    still   without    injury,    except    loss   of   ventilation, 
whereas  a  constant-potential  motor  would  burn  out. 

The  precaution  necessary  is,  never  touch  the  machine 
when  the  current  is  on,  as  the  E,  M.  F.  is  probably  high  and 
very  dangerous.  Turn  off  the  switch  to  fix  the  machine.  A 
constant-current  motor  should  be  provided  with  an  effective 
centrifugal  governor  for  controlling  the  speed  (see  Chapter 
XXXIII);  otherwise  it  will  run  away  and  burst  when  the  load 
is  taken  off,  being  very  much  worse  than  a  series  motor  on  a 


•jo  Practical  Management  of 

constant-potential   circuit,  because   the   latter   reduces   the 
current  as  it  speeds  up,  while  the  former  cannot. 

Battery  Motors. — These  are  nearly  always  series-wound, 
like  the  last,  so  as  to  get  the  most  economical  effect  in  the 
field  when  current  is  weak,  as  this  current  is  expensive  and 
difficult  to  maintain  when  obtained  from  a  primary  battery. 
For  same  reasons,  primary-battery  motors  are  always  for 
small  power  only,  usually  not  exceeding  one-quarter  horse- 
power. If  a  storage-battery  is  used  to  furnish  the  current 
it  is  cheaper  and  gives  more  power,  but  it  requires  frequent 
recharging. 

Dynamotors   (Fig.  39)   are  started   in  the  same  way 


FIG.  39.— 2-H.P.  no-VoLT  INCANDESCENT  ELECTRIC-LIGHT-CIRCUIT 
MOTOR-DYNAMO. 

To  furnish  5000  volts  for  testing  insulation. 

as  motors ;  that  is,  the  motor  portion  of  the  machine  is  con- 
nected to  the  circuit  and  operated  precisely  like  the  corre- 
sponding kind  of  motor.  Usually  the  motor  part  is  plain 


Dynamos  and  Motors.  71 

shunt-wound,  and  is  supplied  with  current  from  a  constant- 
potential  circuit.  It  is  therefore  connected  and  started  in 
the  manner  shown  and  described  on  page  64. 

The  current  generated  by  the  dynamo  portion  of  the 
dynamotor  may  be  taken  from  the  terminals,  and  used  for 
ciny  purpose  to  which  it  is  suited.  The  E.  M.  F.  or  current 
produced  may  be  regulated  by  varying  the  resistance  in  the 
armature  circuit  of  either  the  motor  or  dynamo.  In  case 
the  dynamo  armature  has  a  separate  field-magnet,  the 
E.  M.  F.  and  current  may  be  controlled  by  regulating  the 
magnetic  strength  of  this  field,  or  the  machine  may  be  com- 
pounded or  even  "  over-compounded."  But  if  the  arma- 
tures of  both  motor  and  dynamo  are  acted  upon  by  the 
same  field,  then  the  E.  Ml  F.  of  the  dynamo  cannot  be 
varied  except  by  inserting  resistances  in  the  circuit  of  either 
armature  or  by  shifting  the  brushes.  But  the  latter  will 
be  apt  to  cause  sparking. 

Alternating-Current  Motors. — These  have  not  been 
very  extensively  used  up  to  the  present  time,  although  a 
great  variety  of  forms  have  been  tried  or  suggested.  Al- 
ternating motors  are  required  to  run  on  constant-potential 
circuits,  since  almost  all  alternating-current  systems  are  of 
this  kind.  There  are  several  types  of  these  motors,  the  sim- 
plest of  Avhich  is  a  plain  series  or  shunt  machine,  the  same 
as  for  direct  current,  except  that  the  field-magnet  is  lami- 
nated as  well  as  the  armature  (Fig.  6).  The  trouble  with 
this  type,  which  has  been  used  commercially  in  small  sizes, 
is  that  bad  sparking  is  apt  to  occur  when  the  brush  passes 
from  one  commutator-bar  to  the  next,  and  short-circuits  a 
coil  which  has  alternating  currents  generated  in  it  by  the 
reversals  of  the  field-magnetism.  Various  arrangements 
have  been  devised  to  overcome  this  difficulty,  but  it  is  un- 
likely that  this  type  will  be  practical  in  any  but  small  sizes. 
An  ordinary  alternating-current  dynamo  can  be  used  as  a 
motor,  but  it  must  be  started  and  driven  by  some  other 
motor  or  engine  until  its  speed  is  in  synchronism,  that  is, 
agrees  precisely  with  the  current  alternations  in  order  to 
make  it  run  at  all,  and  then  if  it  loses  this  exact  speed  it 
stops,  and  is  therefore  unpractical  except  for  large  plants. 


72  Practical  Management  of 

Synchronous  motors  of  this  kind  are  sometimes  em- 
ployed in  the  long-distance  transmission  of  power  or  in 
other  special  cases.  Auxiliary  devices  have  been  applied 
to  these  motors  to  start  them  and  bring  them  up  to  syn- 
chronism. Many  other  forms  of  alternating-current  motors 
have  been  brought  out.  So  far,  motors  are  not  used  to  any 
great  extent  on  the  ordinary  (two-wire)  alternating  circuits, 
except  the  small  motors  referred  to  above. 

The  Tesla  and  other  types  of  polyphase  (two  or  three 
phase)  motors  (Fig.  40)  are  operated  by  the  rotation  of 
magnetic  polarity  or  the  so-called  "  rotary  current."  But 


FIG.  40. — TESLA  TWO-PHASE  MOTOR. 

all  of  these  require  special  circuits  of  three  or  four  wires, 
which  have  not  yet  been  introduced  except  for  the  long- 
distance transmission  of  power.  In  fact,  it  is  to  this  pur- 
pose that  polyphase  motors  are  particularly  applicable. 
(See  page  27.)  Some  of  the  smaller  Tesla  induction  motors 
obtain  a  rotary  current  from  a  single  circuit  by  "  splitting 
the  phase." 


Dynamos  and  Motors.  73 

Three-phase  motors  both  of  synchronous  and  induction 
types  are  self-starting.  In  the  latter,  to  get  a  good  torque  in 
starting  or  at  low  speeds,  or  to  start  with  considerable  load, 
it  is  necessary  to  have  added  resistance  in  series  with  the 
armature  winding,  which  consists  merely  of  coils  or  bars  that 
can  be  short-circuited  when  the  machine  has  reached  normal 
speed.  This  resistance  is  gradually  cut  out  by  a  special 
device,  as  the  speed  increases  to  its  full  value.  The  motor 
tends  to  run  almost  synchronously  at  a  certain  speed,  only 
falling  a  few  per  cent  from  no  load  to  full  load.  But  if  the 
motor  is  overloaded  even  for  an  instant,  the  normal  speed 
is  lost  and  the  motor  runs  very  slowly  or  stops  entirely, 
unless  the  load  is  taken  off  or  greatly  reduced,  since  the 
torque  falls  from  its  full  amount  down  to  about  one  third. 
To  start  again  with  the  load  on  the  motor  the  operation  just 
described  must  be  repeated.  When  a  polyphase  motor 
becomes  stalled  in  this  way,  it  is  liable  to  become  overheated 
or  burnt  out. 


74  Practical  Management  of 


CHAPTER   IX. 
DIRECTIONS  FOR  RUNNING  DYNAMOS  AND  MOTORS. 

AFTER  any  one  of  these  machines  has  been  properly 
started,  as  described  in  the  previous  chapters,  it  usually 
requires  vefy  little  attention  while  running ;  in  fact,  a 
dynamo  or  motor  frequently  runs  well  all  day  without  any 
care  whatever. 

In  the  case  of  a  machine  which  has  not  been  run  before 
or  has  been  changed  in  any  way,  it  is  of  course  wise  to 
watch  it  closely  at  first.  It  is  also  well  to  give  the  bear- 
ings of  a  new  machine  plenty  of  oil  at  first,  but  not  enough 
to  run  on  the  armature,  commutator,  or  any  part  that  would 
be  injured  by  it,  and  to  run  the  belt  rather  slack  until  the 
bearings  and  belt  have  gotten  into  easy  working  condition. 
If  possible,  a  new  machine  should  be  run  without  load  or 
with  a  light  one  for  an  hour  or  two,  or  several  hours  in  the 
case  of  a  large  machine ;  and  it  is  always  wrong  to  start  a 
new  machine  with  its  full  load  or  even  a  large  fraction  of  it. 

This  is  true  even  if  the  machine  has  been  fully  tested  by 
its  manufacturer  and  is  in  perfect  condition,  because  there 
may  be  some  fault  in  setting  it  up  or  some  other  circum- 
stance which  would  cause  trouble.  All  machinery  requires 
some  adjustment  and  care  for  a  certain  time  to  get  it  into 
smooth  working  order. 

When  this  condition  is  reached  the  only  attention  re- 
quired is  to  supply  oil  when  needed,  keep  the  machine  clean, 
and  see  that  it  is  not  overloaded.  A  dynamo  requires  that 
its  voltage  or  current  should  be  observed  and  regulated  if 
it  varies.  The  person  in  charge  should  always  be  ready 
and  sure  to  detect  the  beginning  of  any  trouble,  such  as 
sparking,  the  heating  of  any  part  of  machine,  noise,  abnor- 
mally high  or  low  speed,  etc.,  before  any  injury  is  caused, 
and  to  overcome  it  by  following  the  directions  given  in 
Part  III.  Those  directions  should  be  pretty  thoroughly 
committed  to  mind  in  order  to  facilitate  the  prompt  detec- 
tion and  remedy  of  any  trouble  when  it  suddenly  occurs,  as 


Dynamos  and  Motors.  75 

is  apt  to  be  the  case.  If  possible  the  machine  should  be 
shut  down  instantly  when  any  trouble  or  indication  of  one 
appears,  in  order  to  avoid  injury  and  give  time  for  examina- 
tion. 

Keep  all  tools  or  pieces  of  iron  or  steel  away  from  the 
machine  while  running,  as  they  might  be  drawn  in  by  the 
magnetism,  and  perhaps  get  between  the  armature  and  pole- 
pieces  and  ruin  the  machine.  For  this  reason  use  a  zinc, 
brass,  or  copper  oil-can  instead  of  iron  or  "  tin  "  (tinned  iron). 

Particular  attention  and  care  should  be  given  to  the  com- 
mutator and  brushes  to  see  that  the  former  keeps  perfectly 
smooth  and  that  the  latter  are  in  proper  adjustment.  (See 
SPARKING,  p.  120.) 

Never  lift  a  brush  while  the  machine  is  delivering  cur- 
rent unless  there  are  one  or  more  other  brushes  on  the  same 
side  to  carry  the  current,  as  the  spark  might  make  a  bad 
burnt  spot  on  the  commutator. 

Touch  the  bearings  and  field-coils  occasionally  to  see 
that  they  are  not  hot.  To  determine  whether  the  arma- 
ture is  running  hot,  place  the  hand  in  the  current  of  air 
thrown  out  from  it  by  centrifugal  force. 

Special  car?  should  be  observed  by  any  one  who  runs  a 
dynamo  or  motor  to  avoid  overloading  it,  because  this  is  the 
cause  of  most  of  the  troubles  which  occur. 

Personal  Safety. — Never  allow  the  body  to  form  part 
of  a  circuit.  While  handling  a  conductor,  a  second  contact 
may  be  made  accidentally  through  the  feet,  hands,  knees,  or 
other  part  of  body  in  some  peculiar  and  unexpected  manner. 
For  example,  men  have  been  killed  because  they  touched  a 
"  live  "  wire  while  standing  or  sitting  upon  a  conducting 
body. 

Rubber  gloves  (Fig.  41)  or  rubber  shoes,  or  both,  should 
be  used  in  handling  circuits  of  over 
500  volts.     The  safest  plan  is  not  to 
touch   any  conductor  while   the   cur- 
rent is  on,  and  it  should  be  remem- 
bered that  the  current  may  be  present 
when   not   expected,  due  to  an  acci- 
dental contact  with  some  other  wire      FIG.  41.— INSULATING 
or  to  a  change  of  connections.     Tools          RUBBER  GLOVE. 


76 


Practical  Management  of 


with  insulated  handles  (Fig.  410)  or  a  dry  stick  of  wood  should 
be  used  instead  of  the  bare  hand. 


FIG.  410. — TOOLS  WITH  INSULATED  HANDLES. 

The  rule  to  use  only  one  hand  when  handling  dangerous 
electrical  conductors  or  apparatus  is  a  very  good  one,  because 
it  avoids  the  chance,  which  is  very  great,  of  making  contacts 
with  both  hands  and  getting  the  full  current  right  through 
the  body.  This  rule  is  often  made  still  more  definite  by 
saying,  "  Keep  one  hand  in  your  pocket,"  in  order  to  make 
sure  not  to  use  it.  The  above  precautions  are  often  totally 
disregarded,  particularly  by  those  who  have  become  careless 
by  familiarity  with  dangerous  currents.  The  result  of  this 
has  been  that  almost  all  the  persons  accidentally  killed  by  elec- 
tricity have  been  experienced  electric  linemen  or  stationmen. 


Dynamos  and  Motors.  77 


CHAPTER  X. 
DIRECTIONS   FOR   STOPPING  DYNAMOS   AND   MOTORS. 

THIS  is  accomplished  by  following  substantially  the  same 
rules  as  those  given  for  starting  dynamos  and  motors  in 
Chapters  VI,  VII,  and  VIII,  only  in  the  reverse  order. 
But  there  are  certain  peculiar  points  to  be  observed  in  each 
case  ;  so,  in  order  to  avoid  any  possible  mistake,  the  matter 
of  stopping  is  treated  in  this  separate  chapter.  After  any 
machine  is  stopped  it  should  be  thoroughly  cleaned  of  dirt, 
copper  dust,  and  oil,  and  put  in  perfect  order  for  the  next 
run.  This  can  be  done  much  more  easily  while  the  machine 
is  still  warm.  Switches,  brushes,  etc.,  should  be  fixed  so 
that  they  will  not  accidentally  close  the  circuit. 

One  Constant-potential  Dynamo  (Shunt,  or  Com- 
pound Wound)  running  alone  on  a  circuit,  with  no  danger 
of  receiving  current  from  any  other  dynamo  or  bat- 
tery, should  be  slowed  down  and  stopped  without  touching 
the  switches,  brushes,  etc.,  in  which  case  the  E.  M.  F.  and 
current  decrease  gradually  to  zero  as  the  speed  goes  down. 
The  switches  may  then  be  opened  and  the  brushes  lifted 
without  any  spark.  In  the  case  of  copper  brushes  they 
should  be  raised  just  before  the  machine  stops  entirely,  in 
order  to  avoid  any  injury  to  them  if  the  machine  turns 
back  a  little,  as  it  sometimes  does.  Never  switch  out  or 
disconnect  a  dynamo  at  full  or  even  partial  load  except  in 
extreme  emergency,  and  never  raise  the  brushes  while  the 
fields  are  strongly  magnetized,  as  the  discharge  of  the  mag- 
netism may  break  lamps  or  pierce  the  insulation. 

Dynamos  in  Parallel.-—  To  stop  a  dynamo  running  in 
parallel  with  one  or  more  others  or  with  a  storage-battery 
on  the  same  circuit  (usually  constant-potential),  regulate 
its  E.  M.  F.  until  it  is  equal  to  or  only  slightly  greater  than 
that  of  the  circuit,  and  its  amperemeter  shows  that  it  is  pro- 


OF  THK 

UNIVEBSITV 


7  8  Practical  Management  of 

ducing  little  or  no  current ;  then  open  quickly  the  switch 
connecting  its  armature  to  the  circuit.  Under  no  circum- 
stances, however,  should  a  dynamo  in  parallel  with  others 
or  with  a  battery  be  stopped,  slowed  down,  or  have  its  field- 
magnetism  discharged  or  weakened  (i.e.,  more  than  enough 
to  regulate  its  E.  M.  F.,  as  stated)  until  its  armature  is  com- 
pletely disconnected  from  the  circuit,  as  it  might  be  burnt 
out  or  driven  as  a  motor  if  its  E.  M.  F.  decreased  more 
than  a  few  per  cent. 

A  dynamo  should,  of  course,  only  be  thrown  out  of  cir- 
cuit when  the  remaining  machines  are  fully  able  to  carry 
the  load.  Allowance  should  also  be  made  for  any  possible 
increase  in  load. 

Compound-wound     Dynamos     in    Parallel    may    be 

stopped  by  exactly  reversing  the  method  for  starting  (Fig. 
25) ;  but  if,  as  there  suggested,  the  "  equalizer  "  is  left  closed 
all  the  time,  the  machines  may  then  be  stopped  like  simple 
shunt  machines  in  "parallel,  as  just  described. 

Dynamos  on  the  Three-wire  (Direct)  System  are  also 
stopped  like  dynamos  on  any  constant-potential  circuit,  as 
explained  in  the  chapter  on  starting. 

Constant-current  Dynamos  and  Motors  in  series  may 
be  cut  out  of,  or  into,  the  circuit  without  trouble,  and  may 
be  slowed  down  or  stopped  without  dis- 
connecting them  from  the  circuit,  as  the 
current  is  limited.  If  desired,  the  arma- 
ture or  field-coils  may  be  short-circuited 
to  stop  the  action  of  the  machine.  The 
only  precaution,  and  that  is  absolutely 
imperative,  is  to  maintain  the  continuity 
of  the  circuit  and  never  attempt  to  open 
it  at  any  point,  as  it  would  cause  a  dan- 
gerous arc.  Hence  to  stop  a  constant 
FlG'  42cT7T^CUT~  current  motor  it  must  be  cut  out  by  first 

OUT  oWITCH.  i         .  •,  ...  .          * 

closing  the  mam  circuit  around  or  past 
the  machine,  and  then  entirely  disconnecting  both  its  wires 
or  terminals  from  the  circuit.  This  entire  operation  is  ac- 
complished by  any  arc-circuit  cut-out  switch  (Fig.  42). 


Dynamos  and  Motors.  79 

One  Alternator  running  alone  on  a  circuit  may  be 
stopped  or  the  field  current  shut  off  without  trouble. 

Alternators  in  Parallel  may  be  thrown  out  of  circuit  by 
disconnecting  them  one  at  a  time,  the  £.  M.  F.  of  the  par- 
ticular dynamo  having  been  previously  regulated  so  that  it 
is  supplying  only  a  little  current  to  the  circuit. - 

A  Constant-potential  Motor  is  stopped  by  turning  the 
starting-box  handle  back  to  the  position  it  had  before  start- 
ing (Fig.  33),  or  if  there  is  a  switch  Q  connecting  the  motor  to 
the  circuit  it  should  be  opened,  after  which  the  starting-box 
handle  should  be  turned  back  to  be  ready  for  starting  again. 

A  constant-potential  motor,  like  the  corresponding  dyna- 
mos when  in  parallel,  should  never  be  stopped  by  overload 
or  much  reduced  in  speed,  or  have  its  field  discharged  or 
weakened,  until  it  is  disconnected  from  the  circuit ;  other- 
wise its  counter  E.  M.  F.  is  not  enough  to  prevent  an 
excessive  current  from  rushing  through  its  armature. 

Thus  it  will  be  seen  that  the  constant-potential  machine 
is  exactly  the  opposite  of  the  constant  current.  The  former 
is  safest  when  th<!  circuit  is  open,  and  it  is  very  bad  to  short- 
circuit  or  stop  it  with  the  current  on,  whereas  the  circuit  of  the 
latter  should  always  be  kept  closed,  and  the  machine  maybe 
stopped  or  short-circuited  while  in  circuit.  But  the  dynamo 
supplying  the  circuit  should  have  an  effective  regulator  to 
maintain  the  current  at  constant  strength  when  lamps  or 
motors  are  cut  into  or  out  of  the  circuit. 

Waterproof  Covers  of  oiled  canvas  or  enamel  cloth 
should  be  placed  upon  any  machine  when  not  running,  it 
having  been  previously  cleaned,  and  all  dirt,  copper  dust, 
and  superfluous  oil  removed. 


80  Practical  Management  of 


PART  II. 
Examination,  Measurement,  and  Testing^ 

Directions  for  Inspecting  and  Testing  Dynamos  and  Motors  Critically* 


CHAPTER  XL 
INTRODUCTION  AND  CLASSIFICATION. 

THE  matter  of  testing  dynamos  and  motors  critically  is 
of  special  importance,  since  it  is  only  by  a  thorough  test  that 
either  the  manufacturer  or  the  user  can  determine  whether 
a  machine  is  up  to  the  standard.  Nevertheless  it  is  difficult, 
if  not  impossible,  to  find  in  books  or  journals  anything  like 
a  complete  and  practical  system  for  this  purpose.  Each 
electrical  manufacturer  or  engineer  has  collected  by  experi- 
ence certain  methods,  but  these  usually  apply  to  particular 
forms  of  machine  or  testing  apparatus,  and,  moreover,  are 
often  guarded  as  trade  secrets. 

The  following  methods  cover  the  various  points  about 
dynamos  and  motors  which  one  is  likely  to  want  to  test. 
Under  each  heading  exact  methods  are  given,  which  should, 
of  course,  always  be  preferred.  Wherever  possible,  we  have 
also  given  simple,  rough  methods  for  emergencies  or  cases 
in  which  dynamos  or  motors  may  have  to  be  tested  without 
the  accurate  and  expensive  instruments  required  for  the 
more  refined  methods. 

This  subject  differs  from  that  which  is  treated  in  Part 
III,  "  Locating  and  Remedying  Troubles  in  Dynamos  or 
Motors,"  in  that  the  latter  relates  to  actual  faults  which  are 
already  apparent,  whereas  testing  applies  to  any  machine 
whether  in  perfect  working  condition  or  containing  some 
latent  fault  which  a  test  brings  out  or  anticipates.  The  test- 
ing methods  here  given  can  also  be  used  as  supplementary 
to  the  methods  for  locating  troubles  .in  cases  where  a  more 


Dynamos  and  M.  8l 


complete  investigation  may  be  desiraBTev-ftrtesting  any 
machine  it  is  well  to  follow  as  nearly  as  possible  the  direc- 
tions given  by  its  maker  and  try  it  under  the  conditions  for 
which  it  is  intended,  in  regard  to  voltage,  current,  speed,  etc. 
Tests  of  dynamos  and  motors  may  cover  any  or  all  of  the 
following  points  : 

CHAPTER  XII. 

1.  Adjustment  and  fit  of  parts. 

2.  Mechanical  Strength  of  parts  against  breaking  or 
displacement. 

3.  Friction  of  bearings  and  brushes. 

4.  Balance  of  armature  and  pulley. 

5.  Noise. 

6.  Heating    of    armature,   commutator,    field-magnets, 
bearings,  etc. 

7.  Sparking  at  commutator. 

CHAPTER  XIII. 

8.  Electrical  Resistance  of  conductors  and  insulation 
of  machine. 

9.  Line  or  Circuit  testing  for  conductivity,  insulation, 
faults,  etc. 

CHAPTER  XIV. 

10.  Voltage,  E.  M.  F.,  "  drop,"  or  fall  of  potential,  etc. 

11.  Current  in  field  and  in  armature,  free  and  loaded. 

CHAPTER  XV. 

12.  Speed  of  armature,  free  and  loaded. 

13.  Torque  or  pull,  standing  or  running. 

CHAPTER  XVI. 

14.  Power,  electrical  and  mechanical. 

15.  Efficiency,  electrical  and  commercial. 

CHAPTER   XVII. 

16.  Magnetism,—  total  flux,  intensity,  leakage,  and  dis- 
tribution. 

17.  Separation  of  losses  which  occur  in  a  dynamo  or 
motor.      Friction,    resistance,    field    excitation,    hysteresis, 
Foucault  currents,  etc. 


82  Practical  Management  of 


CHAPTER  XII. 

ADJUSTMENT,     MECHANICAL      STRENGTH,     FRICTION, 
BALANCE,  NOISE,  HEATING,  AND   SPARKING. 

i.  Adjustment  ^nd  the  other  points  which  depend  merely 
upon  mechanical  construction  are  hardly  capable  of  being 
investigated  by  a  regular  quantitative  test,  but  they  am  and 
should  be  determined  by  thorough  inspection.  In  fact  a 
very  careful  examination  of  all  parts  of  a  machine  should 
always  precede  any  test  of  it.  This  should  be  done  for  two 
reasons  :  first,  to  get  the  machine  into  proper  condition  for 
a  fair  test ;  and,  second,  to  determine  whether  the  materials 
and  workmanship  are  of  the  best  quality  and  satisfactory  in 
every  respect.  A  loose  screw  or  connection  might  interfere 
with  a  good  test,  and  a  poorly  fitted  bearing,  brush-holder, 
etc.,  might  show  that  the  machine  was  badly  made. 

If  it  is  necessary  to  take  the  machine  apart  for  cleaning 
or  inspection,  the  greatest  care  should  be  exercised  in  mark- 
ing, numbering,  and  placing  the  parts  in  order  to  be  sure  to 
get  them  together  in  exactly  the  same  position  as  before. 
In  taking  a  machine  apart  or  putting  it  together  only  -the 
minimum  force  should  be  used.  Much  force  usually 


FIG.  43. — RAWHIDE  MALLET. 

that  something  wrong  is  being  done.  A  wooden  or  rawhide 
mallet  (Fig.  43)  is  preferable  to  an  iron  hammer,  since  it 
does  not  bruise  or  mar  the  parts  so  much.  Usually  screws, 
nuts,  and  other  parts  should  be  set  up  fairly  tight,  but  not 


Dynamos  and  Motors.  83 

tight  enough  to  run  any  risk  of  breaking  or  straining  any- 
thing. Shaking  or  trying  each  screw  or  other  part  with  a 
wrench  or  screw-driver  will  almost  always  show  whether  any 
of  them  are  too  loose,  or  otherwise  out  oi  adjustment. 

2.  Mechanical  Strength  of  a  dynamo  or  motor  is  best 
specified  by  stating  that  it  should  be  above  question.     The 
base,  bearings,  shaft,  armature,  field-magnets,  and  other  main 
parts  of  the  machine  should  not  spring  even  one  one-hun- 
dredth of  an  inch  with  any  reasonable  force  that  may  be  ap- 
plied to  them.     There  has  long  existed  a  craze  for  very  light 
dynamos  and  motors,  as  a  result  of  which,  strength,  rigidity, 
durability,  and  satisfactory  qualities  in  general  have  been 
sacrificed  to  reduce  weight.     There  is  certainly  no  sense  in 
this.     For  stationary  machines,  and  even  for  ship  dynamos 
or  railway  motors,  good  solid  frames,  bearings,  etc.,  are  much 
better  than  light  ones. 

The  magnetic  attraction  between  the  field  and  armature 
is  often  very  great,  and  amounts  to  hundreds,  or  even  thou- 
sands of  pounds.  This  tends  to  draw  the  pole-pieces  against 
the  armature,  or  to  spring  the  armature  shaft  if  the  armature 
is  even  slightly  nearer  one  pole-piece  than  the  other.  It  is 
well  to  magnetize  the  field  by  putting  the  proper  current 
through  its  coils  and  see  if  it  produces  any  reduction  of  the 
clearance  or  any  displacement  that  is  appreciable  to  the  eye, 
or  even  to  ordinary  measurement.  The  effect  of  the  maxi- 
mum pull  of  the  belt  or  of  any  other  legitimate  stress  may 
be  tested  in  the  same  way. 

In  addition  to  this,  all  the  parts  of  the  machine  should 
be  scrutinized  to  see  if  they  are  of  adequate  size  and  proper 
proportion. 

3.  Friction. — The  friction  of  the  bearings  and  brushes 
can  be  tested  roughly  by  merely  revolving  the  armature  by 
hand  and  noting  if  it  requires  more  than  the  normal  amount 
of  force.     Excessive   friction   is   quite  easily  distinguished, 
even    by    inexperienced    persons.     Another   method    is   to 
cause  the  armature  to  revolve  by  hand  or  otherwise,  and  see 
if  it  continues  to  revolve  by  itself  freely  for  some  time.     A 
well-made  machine  in  good  condition  and  running  at  or  near 


84  Practical  Management  of 

full  speed  will  continue  to  run  for  one  or  more  minutes  after 
the  turning  force  is  removed. 

A  method  for  actually  measuring  the  friction  consists  in 
attaching  a  lever  (a  bar  of  wood,  for  example)  to  the  shaft 
or  pulley  at  right  angles  to  it.  The  force  required  to  over- 
come the  friction  and  turn  the  armature  without  current  is 
then  determined  by  known  weights  or,  more  conveniently, 
by  an  ordinary  spring-balance.  For  convenience  in  dividing 
by  the  length  of  the  lever,  etc.,  to  determine  the  value  of 
the  friction  compared  with  the  power  of  the  machine,  it  should 
be  exactly  I,  2,  or  4  feet  long.  (See  No.  13,  "  Torque.")  The 
friction  of  the  bearings  alone — that  is,  the  pull  required  to 
turn  the  armature  when  the  brushes  are  lifted  off  the  com- 
mutator— should  not  exceed  about  2  p^r  cent  of  the  total 
torque  or  turning  force  of  the  machine  at  full  load.  When 
the  brushes  are  in  contact  with  the  commutator  with  the 
usual  pressure,  the  friction  should  then  not  exceed  about  3 
per  cent,  that  is,  the  brushes  themselves  should  not  consume 
more  than  I  per  cent  of  the  total  turning  force. 

Another  method  of  measuring  the  friction  of  a  machine 
is  to  run  it  by  another  machine  used  as  a  motor,  and  deter- 
mine the  volts  and  amperes  required,  first  with  brushes 
lifted  off,  and  second  with  brushes  on  the  commutator  with 
the  usual  pressure.  The  torque  or  force  exerted  by  the 
driving-machine  is  afterwards  measured  by  a  Prony  brake  in 
the  manner  described  hereafter  for  testing  torque  ;  care  being 
taken  to  make  the  Prony  brake  measurements  at  exactly 
the  same  volts  and  amperes  as  were  required  in  the  friction 
tests.  In  this  way  the  torques  which  were  exerted  by  the 
driving-machine  to  overcome  friction  in  each  of  the  first  two 
tests  are  determined,  and  these  torques,  compared  with  the 
total  torque  of  the  machine  being  tested,  should  give  per- 
centages not  exceeding  those  stated  above  for  the  maximum 
values  of  friction.  The  magnetic  pull  of  the  field  on  the  ar- 
mature may  be  very  great  if  the  latter  is  not  exactly  in  the 
centre  of  the  space  between  the  pole-pieces.  This  would 
have  the  effect  of  increasing  the  friction  of  the  shaft  in  the 
bearings  when  the  field  is  magnetized,  and  occurs  to  a  cer- 
tain extent  in  all  cases,  but  it  should  be  corrected  if  it  be 
comes  excessive.  (See  "  Remedy,  Heating  of  Bearings/ 


Dynamos  and  Motors. 


Cause  9.)  This  may  be  tested  by  turning  the  current  into  the 
fields,  being  sure  to  leave  the  armature  disconnected,  and 
then  turning  the  shaft  with  the  lever  as  before.  The  friction 
in  this  case  should  not  be  more  than  4  OF  5$. 

Tests  for  friction  alone  should  be  made  at  a  low  speed, 
because  at  high  speeds  the  effect  of  Foucault  currents  and 
hysteresis  enter  and  materially  increase  the  apparent  fric- 
tion. (See  No.  17,  "  Separation  of  Losses.") 


l! 


4.  Balance. — The  perfection  of  balance  of  the  armature 
or  pulley  can  be  roughly  tested  by  simply  running  the  ma- 
chine at  its  normal  speed  and  noting  if 
these  parts  are  sufficiently  well  balanced 
not  to  cause  any  objectionable  vibration. 
Of  course  practically  every  machine  pro- 
duces perceptible  vibration  when  running, 
but  this  should  not  amount  to  more  than 
a  very  slight  trembling.  The  balance  of 
a  machine  can  be  definitely  tested  and  the 
extent  of  the  vibration  measured  by  sus- 
pending the  machine  or  mounting  it  on 
wheels  and  running  it  at  full  speed.  In 
this  case  it  is  better  to.  run  the  machine  as 
a  motor,  even  though  it  be  actually  a 
dynamo,  in  order  to  make  it  produce  its 
own  motion,  so  to  speak,  and  avoid  the 
necessity  of  running  it  by  a  belt,  which 
would  cause  vibration  and  interfere  with 
the  test.  If,  however,  the  use  of  a  belt  is 
unavoidable,  it  should  be  arranged  to  run 
vertically  upward  or  downward  so  as  not 
to  produce  any  horizontal  motion  in  ad- 
dition to  the  vibration  of  the  machine 
itself.  Fig.  44  shows  a  machine  hung  up 
to  be  tested  for  balance,  and  run  either  as 
a  motor  or  by  the  vertical  belt,  indicated 
by  a  dotted  line.  Any  lack  of  balance  will  FlG 
cause  the  machine  to  vibrate  or  swing 
horizontally,  and  this  motion  can  be 
measured  on  a  fixed  scale. 


- 


44.  —  ARRANGE- 
MENT FOR  TESTING 
BALANCE  OF  ARMA- 
TURE. 


86  Practical  Management  of 

5.  Noise. — This  cannot  be  well   tested  quantitatively, 
although  it  is  very  desirable  that  a  machine  should  make  as 
little  noise  as  possible.     Noise  is  produced  by  the  various 
causes    given   in  Chapter   XXV,    "  Noise."     The    machine 
should  be  run  at  full  speed,  and  any  noise  and  its  cause  care- 
fully noted.    A  machine  will  nearly  always  run  quieter  alter 
it  has  been  in  use  a  week  or  more>  and  has  worn  smooth, 
especially  the  commutator.     (See  "  Noise,"  Cause  5.) 

6.  Heating. — This  is  measured  by  applying  a  thermom- 
eter to  the  various  parts  of  the  machine   after  it  has  run  at 
full  load  for  one  or  two  hours,  unless  it  is  a  very  large  ma- 
chine, which  will  not  reach  its  maximum   temperature  until 
it  has  run  for  three  or  four  hours.    The  bulb  of  the  thermom- 
eter is  applied  directly  to  the  surface  of  the  field-coil  or  other 
part.     To  test  the  armature  it  must,  of  course,  be  stopped. 
The   thermometer   bulb    should    be    covered    over   with    a 
bunch  of  waste   or   cloth  to  keep   in   the  heat.     The   tem- 
perature of  the  armature,    field-coils,  bearings,  etc.,  should 
not  rise  more  than  45°  C.  or  81°  F.  above  that  of  the  sur- 
rounding air.     A  very  simple   test   of  heating  is  to  apply 
the  hand  to  the  armature,    etc.,  and  if  it  can   be  kept  on 
without  great  discomfort,  the  temperature  is  not  dangerous. 
Allowance   should  always    be  made,  'however,  for  the  fact 
that  on  account  of  its    heat-conductivity  bare    metal   feels 
very  much  hotter  than   cotton-covered  wires,  cloth,  etc.,  at 
the  same  actual  temperatures,  but  this  apparent  difference 
is  much  less  if  the  hand  is  kept  on  for   10  or  20  seconds. 
(See  "  Heating,"  Chapter  XX.) 

7.  Sparking  at  the  commutator  cannot  be  accurately 
measured,  but  it  is  very  ojectionable,  and  in  a  machine  in 
good  order  it  should  be  hardly  perceptible.  In  any  test  one 
should  observe  carefully  whether  the  sparking  is  excessive 
or  not,  and  if  so,  to  what  it  is  due.  (See  "  Sparking,"  Chapter 
XIX.) 

An  approach  to  measurement  may  be  made  by  starting 
with  a  lightly  loaded  machine  and  gradually  increasing  the 
load,  meanwhile  shitting  the  rocker-arm  and  brushes  back  and 
forth,  and  noting  at  what  load  it  is  impossible  to  find  a  non- 
sparking  point.  In  most  machines  the  brushes  must  be 


Dynamos  and  Motors.  87 

shifted  to  follow  the  armature  reaction  as  the  load  increases, 
but  one  should  always  be  able  to  find  a  place  where  spark 
ing  ceases.  A  first-class  machine  should  be  able  to  run 
with  2Q%  overload  before  sparking  is  serious.  If  machine 
begins  to  spark  at  75$  of  its  load,  it  is  clearly  only  three 
quarters  as  useful,  and  this  may  be  taken  in  a  sense  as  a 
measure  of  sparking.  Finely  adjusted  copper  brushes  are 
sometimes  preferred  in  observing  sparking. 


88 


Practical  Management  of 


CHAPTER    XIII. 
ELECTRICAL   RESISTANCE   AND   INSULATION. 

8.  Electrical  Resistance. — There  are  two  principal 
classes  of  resistance  tests  that  have  to  be  made  in  connection 
with  dynamos  and  motors.  First,  the  resistance  of  the  wires 
or  conductors  themselves,  which  might  be  called  the  metallic 
resistance ;  and,  second,  the  resistance  of  the  insulation  of 
the  wires,  which  is  called  the  insulation  resistance.  The 
former  should  usually  be  as  low  as  possible  ;  the  latter  should 
always  be  as  high  as  possible,  because  a  low  insulation  resist- 
ance not  only  allows  current  to  leak,  but  also  causes  "  burn- 
outs "  and  other  accidents.  Metallic  resistance,  such,  for 
example,  as  the  resistance  of  the  armature  or  field-coils,  is 
commonly  tested  either  by  the  Wheatstone  bridge  or  the 
"  drop  "  (fall-of-potential)  method. 

The  Wheatstone  bridge  is  simply  a  number  of  branch 
circuits  connected  as  indicated  in  Fig.  45.  A,  B,  and  C  are 
resistances  the  values  of  which  are  known.  D  is  the  resist- 


FIG.  45. 

ance  which  is  being  measured.     G  is  a  galvanometer,  and  E 
is  a  battery  of  one  or  two  cells  controlled  by  a  key  K,  all 


Dynamos  and  Motors.  89 

being  connected  exactly  as  shown.  The  resistance  C  is 
varied  until  the  galvanometer  shows  no  deflection,  when  the 
key  K  is  closed.  The  value  of  the  resistance  D  is  then  found 
by  multiplying  together  resistances  C  and'j5,  and  dividing  by 

C  X  B 

A  ;  that  is,  D  = — ~ — .      A  very  convenient  form  of  this 
A 

apparatus  is  what  is  known  as  the  portable  bridge  (Fig.  46). 


FIG.'  46. — WHEATS-TONE'S  PORTABLE  BRIDGE  WITH  GALVANOMETER. 

This  consists  of  a  box  containing  the  three  sets  of  known 
resistances  A,  B,  and  C  controlled  by  plugs  ;  also  the  galva- 
nometer G  and  key  K,  all  connected  in  the  proper  way.  In 
some  cases  the  perfection  of  convenience  is  reached  by 
including  the  battery  E  in  the  box  also  ;  but  ordinarily  this 
is  not  done  and  it  is  necessary  to  connect  one  or  two  cells  of 
battery  to  a  pair  of  binding-posts  placed  on  the  box  for  that 
purpose.  Resistances  from  -fa  ohm  to  100,000  ohms  can  be 
conveniently  and  accurately  measured  by  the  Wheatstone 
bridge.  Below  -fa  ohm  the  resistances  of  the  contacts  in  the 
binding-posts  and  plugs  are  apt  to  cause  errors,  and  there- 


90  Practical  Management  of 

fore  special  bridges  provided  with  mercury  contact  cups  are 
used.  In  fact,  in  measuring  any  resistance  care  should  be 
taken  to  make  the  connections  clean  and  tight.  The  or- 
dinary bridge  will  not  measure  above  100,000  ohms,  because 
if  the  resistance  in  the  arm  B  is  100  ohms,  I  ohm  in  A,  and 
1000  ohms  in  C,  then  D  is  100,000.  Sometimes  the  arms  A 
and  B  are  provided  with  looo-ohm  coils  in  addition  to  the 
usual  I,  10,  and  100  ohm  coils  ;  or  sometimes  the  arm  C  con- 
tains more  than  1000  ohms  in  all  ;  in  either  case  the  range 
will  be  correspondingly  increased. 

It  should  be  observed,  however,  that  the  use  of  ratios  of 
1000:  i  or  even  100:1  is  not  desirable,  since  they  are 
likely  to  multiply  any  error  due  to  contact  resistances,  etc. 
In  fact,  it  is  usually  better  to  have  the  four  resistances  not 
very  widely  different  in  value  ;  that  is,  no  one  of  them  should 
be  more  than  ten  times  greater  than  any  other,  except  when 
very  high  or  very  low  resistances  are  to  be  measured.  The 
Wheatstone  bridge  may  be  used  for  testing  the  resistance  of 
almost  any  field-coils  that  are  found  in  practice.  Shunt 
fields  for  no-volt  machines  usually  vary  from  about  100  or 
200  ohms  in  a  i-H.  P.  machine  to  about  5  to  20  ohms  in  a 
IOO-H.  P.  machine.  If  the  voltage  is  higher  or  lower  than 
no,  these  resistances  vary  as  the  square  of  the  voltage. 
Series  fields  for  arc-circuit  dynamos  or  motors  vary  from 
about  I  to  20  ohms.  In  measuring  field  resistances  with  the 
bridge  care  must  be  taken  to  wait  a  considerable  time  after 
pressing  the  battery  key  before  pressing  the  galvanometer 
key,  in  order  to  allow  time  for  the  self-induction  of  the  mag- 
nets to  disappear. 

The  bridge  may  also  be  used  for  testing  the  armature 
resistance  of  most  machines.  But  I  lo-volt  shunt  machines 
above  10  H.  P.  usually  have  resistances  below  TV  ohm,  which 
is  below  the  range  of  the  ordinary  bridge,  as  already  stated. 
Higher  voltage  dynamos  and  motors  have  proportionally 
higher  resistance  armatures.  Arc  machines  have  armatures 
of  about  I  to  20  ohms  resistance,  and  are  therefore  easily 
tested  by  the  bridge. 

The  "  drop  "  or  fall-of- potential  method  is  well  adapted  to 
locating  faults  quickly,  and  to  testing  the  armature  resistance 
of  large  incandescent  dynamos  or  the  resistance  of  contact 


Dynamos  and  Motors.  91 

between  commutator  and  brushes  or  other  resistances  which 
are  usually  only  a  few  hundredths  or  even  thousandths  of 
an  ohm.  This  consists  in  passing  a  current  through  the 
armature  and  connections,  and  a  known-  resistance  of,  say, 
TJF  ohm  connected  in  series  with  each  other,  as  represented 
in  Fig.  47.  The  "  drop  "  or  fall  of  potential  in  the  armature 
and  in  the  known  resistance  are  then  compared  by  connect- 
ing a  galvanometer  first  to  the  terminals  of  the  known 
resistance  (marked  I  and  2),  and  then  to  various  other  points 
on  the  circuit,  as  indicated  by  the  dotted  galvanometer  ter- 
minals at  Mt  N,  O,  Q,  R,  and  S,  so  as  to  include  successively 
all  parts  which  are  to  be  tested.  The  deflections  of  the 
needle  in  all  cases  are  proportional  to  the  resistances  in- 
cluded between  the  points  touched  by  the  terminals  of  the 
galvanometer.  The  current  needed  depends  upon  the 
sensitiveness  of  the  galvanometer,  but  in  any  station  the 
simplest  way  is  to  take  the  current  from  the  mains  or  from 
a  dynamo,  but  then  a  bank  of  lamps  or  a  liquid  resistance 
(see  page  102)  must  be  used  to  limit  the  current,  as  other- 
wise the  parts  being  tested  would  short-circuit  the  dynamo. 

A  much  more  perfect  way  to  obtain  the  current  is  to  use 
a  motor-dynamo  driven  from  the  mains,  as  shown  in  corner 
of  diagram,  and  wound  to  deliver  a  current  at,  say,  6  volts 
for  testing.  There  is  then  no  loss  by  resistances,  and  the 
current  may  be  nicely  regulated  by  moving  the  rocker-arm. 

A  "  station  "  or  a  portable  voltmeter  (page  99)  may  be 
used  for  the  readings,  and  its  terminals  may  be  held  in  the 
hands,  or  they  may  be  conveniently  arranged  to  project  from 
an  insulating  handle  like  a  two-pronged  fork.  Usually  10  to 
TOO  amperes  and  a  voltmeter  reading  to  a  single  volt  or 
fraction  of  a  volt  are  needed  for  low  resistances. 

It  is  wise  to  start  with  a  small  testing  current  and  in- 
crease it  until  a  reasonably  readable  deflection  is  obtained 
on  the  voltmeter.  If  a  current  of  a  number  of  amperes 
cannot  be  had,  a  few  cells  of  storage-battery  or  some  strong 
primary  battery,  such  as  a  Bunsen,  a  bichromate  or  a  plunge 
battery,  can  be  used  with  a  galvanometer. 

The  diagram  indicates  the  testing  of  a  machine  with 
series  fields.  Shunt  fields  must  be  connected  directly  to  the 
line  on  account  of  their  high  resistance,  while  the  armature 


Practical  Management  of 


can  be  connected  as  here  shown,  without  being  allowed  to 
revolve. 

This  drop  method  of  testing  is  very  usefuljn  locating  any 
fault.     The  two  wires  leading  from  the  galvanometer  are 


a 


applied  to  any  two  points  of  the  circuit,  as  indicated  by  the 
dotted  points,  —  for  instance,  to  two  adjacent  commutator- 
bars  or  to  a  brush  tip  and  the  commutator,—  and  any  break 


Dynamos  and  Motors.  93 

or  poor  contact  will  be  immediately  indicated  by  a  corre- 
sponding increase  in  the  deflection  of  the  galvanometer. 
This  shows  that  the  fault  is  between  the  two  points  to  which 
the  galvanometer  wires  are  applied.  Thus,  by  moving  these 
along  on  the  circuit,  the  exact  location  of  any  irregularity, 
such  as  a  bad  contact,  a  short  circuit,  or  an  extra  resistance, 
can  be  found. 

The  insulation  resistance  of  a  dynamo  or  motor,  that 
is,  the  resistance  between  its  wires  and  its  frame,  should  be 
at  least  one  megohm  per  hundred  volts  E.  M.  F.,  and  it  is  of 
course  better  if  it  is  much  higher.  It  is  therefore  beyond 
the  range  of  ordinary  Wheatstohe-bridge  tests,  but  there 
are  two  good  methods  which  are  applicable — the  "  direct- 
deflection  "  method  and  the  voltmeter  method. 

The  direct-deflection  method  is  carried  out  by  connecting  a 
sensitive  galvanometer,  such  as  a  Thomson  high-resistance 
reflecting  galvanometer  (tripod  or  square  pattern),  in  series 
with  a  known  high-resistance,  usually  a  ioo,ooo-ohm  rheo- 


GALVANOMETER 


FIG.  48.— DIRECT-DEFLECTION  METHOD  OF  MEASURING  INSULATION 
RESISTANCE. 

stat,  a  battery,  and  a  key,  as  shown  in  Fig.  48.  The  galva- 
nometer should  be  shunted  with  the  ^^.-coil  of  the  shunt,  so 
that  only  T¥V o  of  tne  current  passes  through  the  galvanome- 
ter, the  machine  being  entirely  disconnected.  The  key  is 
closed  and  the  steady  deflection  noted.  It  is  well  to  use  only 
one  cell  of  battery  at  first,  and  then  increase  the  number  if 
necessary  until  a  considerable  deflection  is  obtained.  The 
circuit  is  then  opened  at  A  and  connected  by  wires  to  the 
binding-post  or  commutator  of  the  dynamo  or  motor  and  to 
the  frame  or  shaft  of  the  machine,  as  indicated  by  dotted 
lines,  so  that  the  insulation  resistance  is  included  directly  in 
the  circuit  with  the  galvanometer  and  battery.  The  key  is 


94  Practical  Management  of 

closed  and  the  deflection  noted.  Probably  there  will  be 
little  or  no  deflection  on  account  of  the  high  insulation 
resistance,  and  the  shunt  is  changed  to  -£-§,  -J,  or  left  out 
entirely  if  little  deflection  is  obtained.  In  changing  the 
shunt,  the  key  should  always  be  open,  otherwise  the  full 
current  is  thrown  on  the  galvanometer.  The  insulation  is 
then  calculated  by  the  formula :  Insulation  resistance  = 

D  X  R  X  >$ 

— ,  in  which  D  is  the  first  deflection  without  the 
a 

machine  connected  and  d  the  deflection  with  the  insulation 
in  the  circuit,  R  the  known  high  resistance,  and  .S  the  ratio 
of  the  shunt.  That  is,  if  the  shunt  is  -^-g-  in  the  first  test 
and  -J-  in  the  second,  then  5  is  100,  and  if  the  shunt  is  out 
entirely  in  the  second  test  5  is  1000.  It  is  safer  to  leave 
the  high  resistance  in  circuit  in  the  second  test  to  protect 
the  galvanometer  in  case  the  insulation  resistance  is  low. 
Therefore  this  resistance  must  be  subtracted  from  the  re- 
sult to  obtain  the  insulation  itself. 


FIG.  49. — WESTON  VOLTMETER. 

By  the  above  method  it  is  possible  to  measure  1000 
megohms,  or  even  more.  The  wires  and  connections  should 
be  carefully  arranged  to  avoid  any  possibility  of  contact  or 
leakage,  which  would  spoil  the  test.  This  test  may  be 
checked  by  placing  one  finger  on  the  shaft  or  frame  and  one 
on  the  binding-post  of  the  machine,  thereby  making 
enough  leakage  to  affect  the  galvanometer  and  show  that 


Dynamos  and  Motors. 


95 


the  connections  are  right,  and  that  any  ptfctf  insulation  will 
be  indicated  if  it  exists. 

The  voltmeter  test  for  insulation  resistance  requires  a  sen- 
sitive high-resistance  voltmeter,  such  as  the  Weston.  Take, 
for  example,  the  I5o-volt  instrument,  Fig.  49,  which  usually 
has  about  15,000  ohms  resistance.  (A  certificate  of^  the 
exact  resistance  is  pasted  inside  each  case.)  Apply  it  to 
some  circuit  or  battery,  and  measure  the  voltage.  This 
should  be  as  high  as  possible  ;  say,  100  volts.  The  insu- 
lation resistance  of  the  machine  is  then  connected  into  the 
circuit,  as  indicated  in  Fig.  50.  The  deflection  of  the  volt- 


Mains 


Voltmeter 


FIG.  50. — CONNECTIONS  FOR  TESTING  INSULATION  WITH  VOLTMETER. 


meter  is  less  than  before,  in  proportion  to  the  value  of  the 
insulation  resistance. 

The  insulation  is  then  found  by  the  equation :  Insula- 
tion resistance^ = R,  in  which  D  is  the  first  and  d 

a 

the  second  deflection,  and  R  the  resistance  of  the  voltmeter. 
If  the  circuit  is  100  volts,  then  D  is  loo  ;  and  if  d,  the  deflec- 
tion through  the  insulation  resistance  of  the  machine,  is  I 
division,  then  the  insulation  is  (100  X  15,000)  —  15,000  = 
1,485,000  ohms.  Permanent  marks  indicating  amounts  of 
insulation  may  be  put  on  the  voltmeter  scale.  The  dyn- 
amo should  then  be  regulated,  when  making  measurements, 
to  the  E.  M.  F.  assumed  in  preparing  this  scale  (say,  1 1 5  volts). 

To  calculate  the  scale,   use  this  formula :  d  —  v  ,  in 

JL  -\-  1\. 

which  X  is  the  resistance  of  insulation  (i  megohm,  J  meg- 


96  Practical  Management  of 

ohm,  etc.),  and  d  is  the  number  of  volts,  opposite  which  the 
corresponding  graduation  is  to  be  placed  to  form  the  new 
scale.  This  method  does  not  test  very  high  resistances,  but 
if  little  or  no  deflection  is  obtained  through  the  insulation  re- 
sistance, it  shows  that  the  latter  is  at  least  several  megohms, 
— which  is  high  enough  for  most  practical  purposes. 

The  ordinary  magneto-electric  bell  may  be  used  to  test 
insulation  by  simply  connecting  one  terminal  to  the  binding- 
post  of  the  machine  and  the  other  to  the  frame  or  shaft. 

A  magneto  bell  is  rated  to  ring  through  from  10,000  to 
30,000  ohms,  and  if  it  does  not  ring,  it  shows  that  the  insu- 
lation is  more  than  that  amount.  This  limit  is  altogether 
too  low  for  proper  insulation  in  any  case,  and  therefore  this 
test  is  rough,  and  really  only  shows  whether  or  not  the 
insulation  is  very  poor  or  the  machine  actually  grounded. 

The  magneto  is  also  used  for  *'  continuity  "  tests,  to  de- 
termine whether  a  circuit  is  complete,  by  simply  connecting 
the  two  terminals  of  the  magneto  to  those  of  the  circuit.  If 
the  bell  can  be  rung,  it  shows  that  the  circuit  is  complete ; 
if  not,  it  indicates  a  break.  An  ordinary  electric  bell  and 
cell  of  battery  can  be  used  in  place  of  the  magneto. 

The  insulation  of  a  machine  should  always  be  tested 
for  disruptive  strength  with  a  current  of  at  least  double  the 
normal  working  pressure,  to  see  if  it  will  "break  down"  or 
be  punctured  by  the  current.  A  motor-dynamo  wound  to 
give  a  very  high  voltage  is  convenient  for  this. 

Tests  of  the  resistances  of  dynamos  or  motors  should 
properly  be  made  when  the  machines  are  as  warm  as  they 
get  when  running  continuously  at  full  load.  This  increases 
the  resistance  of  conductors  and  decreases  the  insulation 
resistance,  but  it  gives  the  actual  working  values  better  than 
a  test  made  when  the  machine  is  cold. 

9.  Line  or  Circuit  Testing  for  conductor  resistance  and 
insulation  resistance  is  performed  by  exactly  the  same  meth- 
ods as  those  just  described  for  making  the  corresponding 
tests  on  dynamos  and  motors.  For  example,  in  testing  the 
insulation  resistance  of  a  line  or  circuit  one  wire  is  connected 
to  the  line  and  the  other  to  the  ground  (a  gas  or  water  pipe 
is  convenient  for  this  purpose),  instead  of  connecting  one 


Dynamos  and  Motors.  97 

wire  to  the  commutator  and  the  other  to  the  frame  of  the 
machine,  as  described  for  testing  the  insulation  resistance  of 
a  dynamo ;  otherwise  the  test  is  exactly  the  same.  The 
"  electrical  capacity  "  of  a  line  will  cause  current  to  flow  into 
it  for  some  seconds  after  the  key  is  closed,  even  though  the 
line  is  well  insulated.  Therefore  one  must  wait  till  the 
galvanometer  needle  comes  to  rest  before  taking  the  reading. 
The  testing  of  circuits  for  current,  voltage,  etc.,  is  also  done 
in  the  same  manner  as  described  in  the  following  chapter 
for  dynamos  and  motors. 


98 


Practical  Management  of 


CHAPTER   XIV. 
VOLTAGE   AND    CURRENT. 

IO.  Voltage. — Unfortunately  a  really  satisfactory  volt= 
meter  is  rather  expensive,  because  it  is  required  to  be  very 
accurate,  an  error  of  one  per  cent  in  the  voltage  of  an  in- 
candescent circuit  being  objectionable,  whereas  the  same 
error  would  be  insignificant  in  almost  any  other  practical 
measurement.  A  voltmeter  should  have  as  high  a  resistance 


FIG.  51.— PRESSURE-INDICATOR  FOR  CENTRAL  STATIONS. 

as  possible — at  least  several  hundreds  or  thousands  of  ohms 
—  in  order  not  to  take  too  much  current,  which  might  lower 
its  reading  on  a  high-resistance  circuit.  It  should  not  be 
affected  by  the  magnetism  of  a  dynamo  or  motor  at  any 


UNIVERSITY 

Dynamos  and 


distance  over  four  or  five  feet.  There  are  two  kinds  of  volt- 
meters :  those  which  simply  indicate  whether  the  E.  M.  F. 
is  at  or  a  little  above  or  below  the  standard  (i  10  volts,  for 
example), — such  instruments  (Fig.  51)  are  generally  used  in 
central  stations,  and  are  called  pressure-indicators, — and 
those  which  measure  from  a  single  volt  or  fraction  up  to  the 
full  capacity  of  the  scale,  such  as  the  Weston  (Fig.  49). 
These  often  have  two  scales,  one  reading  one  tenth  of  the 
other. 

The  voltage  of  any  machine  or  circuit  is  tested  by  merely 
connecting  the  two  binding-posts  or  terminals  of  the  volt- 
meter to  the  two  terminals  or  conductors  of  the  machine  or 
circuit.  In  the  case  of  a  dynamo  or  motor  the  voltmeter  is 
usually  applied  to  the  two  main  binding-posts  or  brushes  of 
the  machine  to  get  the  external  voltage  of  the  machine.  This 
external  voltage  is  what  a  dynamo  supplies  to  the  circuit, 
and  it  is  what  a  motor  receives  from  the  circuit.  This  is 
called  the  pole  difference  of  potential  or  terminal  voltage, 
and  is  the  actual  figure  upon  which  calculations  of  the 
efficiency,  capacity,  etc.,  of  any  machine  are  based. 

A  dynamo  for  constant-potential  circuits  should,  of 
course,  give  as  nearly  as  possible  a  constant  voltage.  A  plain 
shunt  machine  usually  falls  from  5  to  15  per  cent  in  voltage 
when  its  current  is  varied  from  nothing  to  full  load.  This 
is  due  to  the  loss  of  voltage  in  the  resistance  of  the  armature, 
which  in  turn  weakens  the  field  current  and  magnetism  ; 
armature  reaction  and  reduction  in  speed  usually  occur  also, 
and  still  further  lower  the  external  voltage.  This  variation 
is  very  undesirable,  and  is  usually  avoided  by  regulating  the 
field-magnetism  (by  varying  the  resistance  in  the  field  circuit) 
or  by  the  use  of  compound-wound  generators.  A  compound- 
wound  dynamo  should  not  fall  appreciably  from  no  load  to 
full  load ;  in  fact,  if  it  is  "  overcompounded  "  it  should  rise 
3  to  10  per  cent  In  voltage  to  make  up  for  loss  on  the.wiring. 

The  voltage  of  a  constant-current  dynamo  or  motor  is  not 
important.  The  current  should  be  carefully  measured  by 
an  amperemeter,  but  little  or  no  attention  is  paid  to  the 
voltage  in  practical  working ;  in  fact  it  changes  constantly 
with  variations  in  the  load.  But  it  is  necessary,  of  course, 
to  measure  it  in  making  efficiency  or  other  exact  tests. 


ioo  Practical  Managemeat  of 

A  simple  and  fairly  accurate  method  of  measuring  voltage 
is  by  means  of  ordinary  incandescent  lamps.  A  little  practice 
enables  one  to  tell  whether  a  lamp  has  its  proper  voltage 
and  brightness.  In  this  way  it  is  easy  to  tell  if  the  voltage 
is  even  one  or  two  per  cent  above  or  below  the  normal 
point.  Voltages  less  than  the  ordinary  can  be  tested  by 
using  low-voltage  lamps  or  by  estimating  the  brightness  of 
high-voltage  lamps.  For  example,  a  lamp  begins  to  show  a 
very  dull  red  at  one  third  and  a  bright  red  at  one  half  its  full 
voltage.  Voltages  higher  than  that  of  one  lamp  can  be 
tested  in  this  way  by  using  lamps  in  series.  Thus  1000  volts 
can  be  measured  by  using  10  lamps  in  series,  and  so  on. 

ii.  Current. — This  is,  of  course,  measured  by  an  ampere- 
meter (Fig.  52),  which  is  usually  cheaper  than  a  voltmeter, 


FIG.  52. — WESTON  AMMETER. 

because  it  contains  a  comparatively  small  amount  of  wire, 
and  does  not  ordinarily  require  to  be  so  accurate.  In 
testing  the  current  of  a  dynamo  or  motor,  it  is  only  neces- 
sary to  connect  an  amperemeter  of  the  proper  range  in 
series  with  the  machine  to  be  tested,  so  that  the  whole 
current  to  be  measured  passes  through  the  instrument. 
To  test  the  current  in  the  armature  or  the  field  alone,  the 
amperemeter  is  connected  in  series  with  the  particular  part. 
In  the  case  of  a  shunt-wound  dynamo,  it  is  well  to  open 
the  external  circuit  entirely  in  testing  the  current  used  in 


Dynamos  and  Motors.  101 

the  field-coils  in  order  to  avoid  mistake  ;  for  the  same  reason 
the  brushes  of  a  shunt  motor  should  be  raised  while  testing 
the  current  taken  by  the  field.  In  a  constant-current 
(series-wound)  dynamo  or  motor  the  same  current  flows 
through  all  parts  of  the  machine  and  the  circuit,  conse- 
quently the  measurement  of  current  is  very  simple. 

On  constant-current  circuits,  instruments  are  often  used 
which  simply  indicate  whether  the  amperes  are  at  or  near  the 
standard  current  of,  say,  10  amperes,  precisely  as  with 
"station  pressure-indicators"  (Fig.  51).  The  Brush  Am- 
meter (Chapter  XXXI,  Fig.  92)  is  of  this  kind. 

If  an  ammeter  cannot  be  had,  current  may  be  measured  by 
a  voltmeter  by  inserting  a  known  resistance  in  the  circuit 
and  measuring  the  difference  of  potential  between  its  ends 
with  the  voltmeter.  The  volts  so  indicated,  divided  by  the 
resistance  in  ohms,  give  the  number  of  amperes  flow- 
ing. If  a  known  resistance  is  not  at  hand,  the  resistance  of 
a  part  of  the  wire  forming  the  circuit  can  be  computed  from 
its  diameter  measured  with  a  screw  caliper  or  a  wire  gauge, 
by  referring  to  any  of  the  tables  of  resistances  of  wires. 

Or  the  resistance  may  be  measured  by  a  Wheatstone 
bridge  (Fig.  46),  or  by  putting  an  ammeter,  sometime  when 
one  can  be  spared,  into  the  circuit,  while  the  voltmeter  is 
connected.  The  volts  divided  by  the  amperes  give  the 
resistance  in  ohms  between  the  points  to  which  the  voltmeter 
is  connected.  Or  two  connections  can  be  attached  per- 
manently to  two  points  on  the  circuit  and  an  ammeter 
temporarily  inserted,  and  for  every  reading  of  the  ammeter 
the  corresponding  reading  of  the  voltmeter  attached  to  these 
connections  may  be  noted.  Then,  by  keeping  a  list  of  these 
readings,  the  amperes  can  be  found  at  any  future  time,  by 
connecting  the  voltmeter  to  the  two  permanent  contacts. 
This  preliminary  use  of  the  ammeter  amounts  to  measuring 
the  resistance  between  the  two  contacts,  but  allows  for  the 
increase  of  resistance  when  the  current  and  heating  increase. 
In  any  case,  it  is  convenient  to  use  a  length  of  wire,  or  a 
distance  between  contacts  which  will  give  an  even  amount 
of  resistance,  say  ^  or  yj^  ohm.  And  as  with  large  cur- 
rent the  resistance  will  be  fractional,  care  must  be  taken 
to  avoid  errors  in  multiplying,  etc.  Current  may  also  be 


IO2  Practical  Management  of 

very  roughly  judged  by  the  temperature  of  the  wire,  or  by 
the  size  of  wire  necessary  to  carry  it  without  exceeding  a 
certain  temperature. 

As  the  pressure  of  the  circuit  is  constant  in  most  cases 
where  ammeters  are  used  to  indicate  the  current  drawn, 
a  definite  number  of  amperes  represents  I  H.  P.  and  the 
dial  may  be  graduated  in  H.  P.  as  well  as  amperes. 

Thus  on  ii5-volt  circuits  6.48  amperes  is  I  H.  P.  of 
current  (or  746  watts),  12.96  amperes  is  2  H.  P.,  etc.  On 
5OO-volt  circuits  1.49  amperes  is  I  H.  P.,  etc.  (See  section  14, 
"  Power.") 

In  testing  the  output  of  a  dynamo,  it  is  often  quite  a 
problem  to  dispose  of  the  current  produced.  A  bank  of 
lamps,  for  example,  to  use  the  whole  current  generated  by 
a  dynamo  of  1 10  volts  and  200  amperes  would  be  very 
expensive.  A  sufficient  number  of  resistance-boxes  for  the 
purpose  would  also  be  very  costly.  The  best  way  is  to  use 
its  current  to  drive  a  motor  which  is  belted  back  to  the 
dynamo.  In  this  way  most  of  the  power  is  returned  instead 
of  being  wasted.  If  a  motor  cannot  be  had,  the  simplest  and 
cheapest  way  to  consume  a  large  current  is  to  place  two 
plates  of  iron  in  a  common  tub  or  trough  filled  with  a  solu- 
tion of  carbonate  of  soda  (common  washing-soda)  which  is 
much  better  than  almost  any  other  solution,  because  it 
neither  gives  off  fumes  nor  eats  the  electrodes.  The  main 
conductors  are  connected  to  the  two  plates,  respectively, 
and  the  current  passes  through  the  solution.  The  resistance 
and  current  are  regulated  by  varying  the  distance  between 
the  plates,  the  depth  they  are  immersed  in  the  liquid  and  the 
strength  of  the  solution.  The  energy  may  be  sufficient  to 
boil  the  liquid,  but  this  does  no  harm.  Three  to  ten 
amperes  per  square  inch  of  active  surface  of  plate  may  be 
allowed. 


Dynamos  and  Motors. 


CHAPTER   XV. 
SPEED   AND  TORQUE. 

12.  Speed. — This  is  usually  measured  by  the  well-known 
speed-counter  (Fig.  53),  which   consists  of  a  little  spindle 


FIG.  53. — SPEED-COUNTER. 

which  turns  a  wheel  one  tooth  each  time  it  revolves.  The 
point  of  the  spindle  is  held  against  the  centre  of  the  shaft 
of  the  dynamo  or  motor  for  a  certain  time,  say  one  minute 
or  one-half  minute,  and  the  number  of  revolutions  is  read 
off  from  the  position  of  the  wheel. 

Another  instrument  for  testing  the  number  of  revolutions 
per  minute  is  the  tachometer.  The  stationary  form  of  this 
instrument  is  shown  in  Fig.  54-  This  requires  to  be  belted 
by  a  string,  tape,  or  light  leather  belt  to  the  machine  the 
speed  of  which  is  to  be  tested.  If  the  sizes  of  the  pulleys 
are  not  the  same,  their  speeds  are  inversely  proportional  to 
their  diameters.  The  portable  form  of  this  instrument  (Fig. 
55)  is  applied  directly  to  the  end  of  the  shaft  of  the  ma- 
chine, like  the  speed-counter.  The  tip  can  be  slipped  upon 
either  one  of  the  three  spindles,  which  are  geared  together, 
according  as  the  speed  is  near  500,  1000,  or  2000  revolutions. 
These  instruments  possess  the  great  advantage  over  the 
speed-counter  that  they  instantly  point  on  the  dial  to  the 


104 


Practical  Management  of 


proper  speed,  and  they  do  not  require  to  be  timed  for  a  cer- 
tain period. 

A  simple  way  to  test  revolutions  per  minute  is  to  make 
a  large  black  or  white  mark  on  the  belt  of  a  machine  and 
note  how  many  times  the  mark  passes  per  minute ;  the 


FIG.  54. — STATIONARY  TACHOMETER. 


FIG.  55. — PORTABLE  TACHOMETER. 

length  of  the  belt  divided  by  the  circumference  of  the  pulley 
gives  the  number  of  revolutions  of  the  pulley  for  each  time 
the  mark  passes.  The  number  of  revolutions  of  the  pulley 
to  one  of  the  belt  can  also  be  easily  determined  by  slowly 
turning  the  pulley  or  pulling  the  belt  until  the  latter  makes 
one  complete  trip  around,  at  the  same  time  counting  the 


Dynamos  and  Motors.  105 

revolutions  of  the  pulley.  If  the  machine  has  no  belt,  it  can 
be  supplied  with  one  temporarily  for  the  purpose  of  the  test, 
a  piece  of  tape  with  a  knot  or  an  ink-mark  being  sufficient. 
Care  should  be  taken  in  all  these  tests  of  speed  with  belts 
not  to  allow  any  slip ;  for  example,  in  the  case  of  the  tape 
belt  just  referred  to,  it  should  pass  around  the  pulley  of  the 
machine,  and  some  light  wheel  of  wood  or  metal  which  turns 
so  easily  as  not  to  cause  any  slip  of  the  belt  on  the  pulley  of 
the  machine. 

13.  Torque  or  Pull  is  measured  in  the  case  of  a  motor  by 
the  use  of  a  Prony  brake.  This  consists  of  a  lever  LL  of 
wood  clamped  on  to  the  pulley  or  shaft  of  the  machine  to 
be  tested,  as  indicated  in  Fig.  56.  The  pressure  of  the 
screws  6"  S  is  then  adjusted  by  the  wing-nuts  until  the  friction 
of  the  clamp  on  the  pulley  is  sufficient  to  cause  the  motor 


FIG.  56. — PRONY  BRAKE  FOR  MEASURING  TORQUE  OR  PULL. 

to  take  a  given  current  and  run  at  a  given  speed.  Usually 
the  maximum  torque  or  pull  is  the  most  important  to  test, 
and  this  is  obtained  in  the  case  of  a  constant-potential 
motor  by  tightening  the  screws  5  5  until  the  motor  draws  its 
full  current  as  indicated  by  an  amperemeter.  What  the  full 
current  should  be,  is  usually  marked  on  the  name  plate;  if 
not,  it  may  be  assumed  to  be  about  8  amperes  per  H.  P.  for 
iio-volt  motors,  4  amperes  per  H.  P.  for  22o-volt,  and  if 


io6  Practical  Management  of 

amperes  per  H.  P.  for  5oo-volt  motors.  If  the  machine  is 
rated  in  kilowatts,  the  full  current  in  amperes  can  be  found 
by  multiplying  by  IOOO,  and  dividing  by  the  voltage  of  the 
machine.  The  torque  or  pull  is  measured  by  known  weights, 
or  more  conveniently  by  a  spring  balance  P.  If  desired, 
the  test  may  also  be  made  at  three  quarters,  one  half,  or 
any  other  fraction  of  the  full  current. 

The  torque  or  pull  in  pounds  which  should  be  obtained 
may  also  be  calculated  from  the  power  at  which  the  ma- 
chine is  rated  by  the  formula 

H.  P.  X  33,ooo 
6.28X5" 

in  which  H.  P.  is  the  horse-power  of  the  machine  at  full  load, 
and  6"  is  the  speed  of  the  machine  in  revolutions  per  minute 
at  full  load.  Torque  is  given  at  unit  radius,  commonly 
pounds  at  one  foot.  The  pull  at  any  other  radius  is  con- 
verted into  torque  by  multiplying  by  the  radius.  I,  2,  and 
4  ft.  are  convenient  radii  or  lengths  of  lever  for  measuring 
pull.  One  H.  P.  produced  at  a  speed  of  1000  requires  a 
pull  of  5.252  Ibs.  at  end  of  i-ft.  lever;  at  500  revolutions, 
twice  as  much  ;  at  2000  revolutions,  half  as  much  ;  and  so  on. 
If  lever  is  4  feet  long,  the  pull  is  one  fourth  as  much,  etc. 

The  torque  of  a  constant-current  motor  is  found  by  ad- 
justing the  screws  .S.S  until  the  armature  runs  at  its  normal 
speed. 

The  Torque  of  a  Dynamo,  that  is,  the  force  required  to 
drive  it,  is  tested  by  a  transmission  dynamometer.  This 
is  a  machine  which  measures  the  pull  on  the  belt  or  the 
turning  power  of  the  shaft,  without  interfering  with  the 
motion.  There  are  several  forms  of  this  apparatus,  but 
none  of  them  are  very  satisfactory.  In  the  cradle  dynamom- 
eter the  dynamo  is  placed  on  a  platform,  which  is  hung  on 
a  pivot  or  fulcrum.  The  axis  of  the  shaft  of  the  dynamo  is 
adjusted  so  that  it  exactly  coincides  with  the  axis  of  the 
pivot.  When  the  dynamo  is  run  by  a  vertical  belt,  the  pull 
or  torque  tends  to  cause  the  dynamo  to  turn  about  its  axis 
of  suspension,  and  the  force  of  this  torque  is  measured  by 
the  amount  of  weights  required  to  keep  the  dynamo  and 
platform  horizontal.  In  a  modified  form  of  the  cradle  dyna- 


Dynamos  and  Motors. 


707 


mometer  the  dynamo  is  placed  in  a  water-tight  DOX  which 
floats  in  another  box  filled  with  water  instead  of  being  hung 
on  a  pivot.  A  simple  testing-room  dynamometer  is  shown 
in  Fig.  57.  The  belt  from  the  motor  passes  around  two 


FIG.  57. — WHEELER  TRANSMISSION  DYNAMOMETER. 

fdlers,  and  then  around  the  driven  pulley,  which  carries  a 
large  fan,  or  may  be  connected  to  other  work.  The  idlers 
are  on  a  beam  pivoted  on  the  shaft  of  the  driven  pulley. 
AJ  they  are  equidistant  from  this  pivot,  the  only  force  to 
move  the  beam  is  that  imparted  to  the  belt  by  the  motor. 
This  is  measured  by  the  spring  balance  which  is  attached  to 
a  right-angle  lever,  to  which  is  also  connected  a  dash-pot  to 
check  the  vibration  of  the  spring  balance  while  the  belt  is 
in  motion.  For  further  information  on  this  subject,  the 
reader  is  referred  to  "  Dynamometers,  and  the  Measurement 
of  Power,"  by  J.  J.  Flather. 

It  is  usually  much  easier  to  test  the  torque  of  a  dynamo 
by  running  it  as  a  motor  and  testing  it  by  the  Prony  brake 
method  described  above. 

The  torque  of  a  dynamo  is  practically  equal  to  that  of  a 
motor  under  identical  conditions. 


Practical  Management  of 


CHAPTER   XVI. 
POWER  AND   EFFICIENCY. 

14.  Power.  —  The  electrical  power  of  a  dynamo  or  motor 
is  found  by  testing  the  voltage  and  current  at  the  terminals 
of  the  machine,  as  described  in  sections  10  and  n,  and  mul- 
tiplying the  two  together,  which  gives  the  electrical  power 
of  the  machine  in  watts.  Watts  are  converted  into  horse- 
power by  dividing  by  746,  and  into  kilowatts  by  dividing  by 
1000. 

The  mechanical  power  of  a  dynamo  or  motor,  that  is, 
the  power  required  for  or  developed  by  it,  is  found  by  mul- 
tiplying its  pull,  determined  as  described  in  section  13,  by 
its  speed,  determined  as  described  in  section  12,  and  by  the 
circumference  of  the  circle  on  which  the  pull  is  measured, 
and  dividing  by  33,000.  That  is, 

PXSX6.2SXR 
Horse-power  =         ~ 


in  which  P  is  the  pull  in  pounds,  5"  the  speed  in  revolutions 
per  minute,  and  R  the  radius  in  feet  at  which  Pis  measured. 

15.  Efficiency.  —  This  is  determined  in  the  case  of  a 
dynamo  by  comparing  the  mechanical  power  required  to 
drive  it  by  the  electrical  power  generated  by  it;  that  is, 

^r~  .  f  .  Electrical  power 

Efficiency  of  dynamo  •=  ^=  —  =  -  :  —  ~    —  . 

Mechanical  power 

The  efficiency  of  a  motor  is  the  mechanical  power  de- 
veloped by  it  divided  by  the  electrical  power  supplied  to  it  ; 
that  is, 

T-nr-  •  f  Mechanical  power 

Efficiency  of  motor  =  -  -  . 

Electrical  power 


Dynamos  and  Motors. 


109 


These  are  the  actual  or  commercial  efficiencies  of  these 
machines,  and  should  be  about  90  per  cent  in  machines  of 
10  H.  P.  and  over. 

The  so-called  "  electrical  efficiency  "  is  misleading  and  of 
little  practical  importance,  and  should  not  be  considered  in 
commercial  work.  The  mechanical  and  electrical  power  in 
the  above  equations  are  determined  as  described  in  the  last 
section. 


AMPERES  REQUIRED  TO  GIVE  DIFFERENT  POWERS,  ON  THE  VARIOUS 
CONSTANT-POTENTIAL  CIRCUITS,  ALLOWING  FOR  THE  EFFICIENCY  OF 
THE  ORDINARY  MOTOR. 


Horse- 
power 
of 
Motor. 

Effi- 
ciency 
of 
Motor. 

Electrical 
H.  P. 
Required. 

On  8-volt 
Battery 
Circuit. 

On  75-volt 
Circuit. 

On  no-volt 
Circuit. 

On  22o-volt 
Circuit. 

On  5oo-volt 
Circuit. 

Ampere. 

Amperes. 

Amperes. 

Amperes. 

Amperes. 

A 

4o£ 

.16 

14 

1.6 

I.I 

•53 

•23 

i 

55 

•23 

21 

2.2 

1-5 

.76 

•34 

1 

60 
62 

.28 
.40 

26 

38 

2.8 

4-0 

1.9 

2.7 

•95 
1.4 

.41 
.60 

* 

66 

.76 

71 

7-5 

5-1 

2.6 

1-13 

I 

72 

i-4 

130 

13-8 

9.4 

4-7 

2.07 

2 

75 

2.7 

26.6 

iS.i 

9.1 

3-98 

3 

78 

3-8 

38.2 

26. 

13-0 

5-73 

4 

79 

5-0 

50.3 

34.3 

17.2 

7-55 

5 

80 

6.2 

62.2 

42.4 

21.2 

9-33 

1\ 

82 

9.1 

90.9 

62. 

31.0 

13.6 

10 

84 

12. 

118. 

80.7 

40.4 

17.8 

15 

85 

I7.6 

176. 

1  20. 

60. 

26.3 

20 

86 

23. 

231- 

158. 

79- 

34-7 

25 

88 

28. 

283. 

193. 

96. 

42.4 

30 

88 

34- 

339- 

231. 

116. 

50.7 

35 

89 

40. 

391- 

266. 

133. 

59- 

40 

89 

45- 

447- 

305. 

153- 

67- 

50 

90 

55-5 

553- 

377- 

1  88. 

83. 

75 

90 

83- 

828. 

565. 

283. 

124. 

IOO 

90 

in. 

1107. 

754- 

377- 

1  66. 

It  is  usually  more  convenient  to  test  the  efficiency  of  a 
dynamo  by  testing  it  as  a  motor  with  a  Prony  brake.  But 
the  efficiency  of  a  dynamo  may  be  determined  very  nicely 
by  driving  it  with  a  calibrated  electric  motor,  that  is,  one  in 


1 1  o  Practical  Management  of 

which  the  power  developed  for  any  given  number  of  volts 
and  amperes  consumed  is  known  (section  14).  Then  it  is 
only  necessary  to  measure  the  watts  generated  by  the  dyn- 
amo when  the  motor  is  running  at  a  certain  power,  and  the 
efficiency  of  the  dynamo  is  the  watts  divided  by  the  known 
power.  Another  method  is  to  employ  two  identical  machines, 
one  used  as  a  motor  driving  the  other  as  a  dynamo.  The  shafts 
of  the  two  machines  should  be  directly  connected  by  some 
form  of  coupling;  a  belt  may  be  used,  but  its  friction  would 
cause  a  small  loss.  The  watts  generated  by  the  dynamo 
divided  by  the  watts  consumed  by  the  motor  is  the  com- 
bined efficiency  of  the  two  machines,  and  the  efficiency  of 
each  is  the  square  root  of  that  fraction.  For  example,  if  the 
combined  efficiency  is  .81,  then  that  of  each  is  .90.  since 
.90  X  .90  —  .81.  This  assumes  that  the  two  efficiencies  are 
equal,  which  is  sufficiently  correct  if  the  machines  are  ex- 
actly alike.  The  current  generated  by  the  dynamo  may  be 
used  to  help  feed  the  motor,  and  then  only  the  difference  in 
current  need  be  supplied  by  another  dynamo  or  other 
source.  This  latter  current  represents  the  inefficiency  or 
losses  from  friction,  etc.,  in  both  machines. 

To  test  in  this  way,  connect  both  machines  in  multiple- 
arc  with  the  source  of  current,  belt  them  together,  and  then 
weaken  the  field,  or  shift  the  brushes  of  the  machine  which 
is  to  be  used  as  a  motor,  so  that  it  will  speed  up  and  drive 
the  other  as  a  dynamo,  or  cause  it  to  drive  the  other  by 
putting  a  larger  pulley  on  it.  In  this  way  the  motor  will 
consume  current  from  the  circuit  while  the  dynamo  yields 
current  to  the  circuit.  Both  currents  are  measured  and  the 
efficiencies  calculated. 

The  efficiency  of  a  dynamotor  or  direct-current  trans- 
former is  very  easily  determined  by  simply  measuring  the 
input  and  output  in  watts  (by  wattmeters  or  by  ampere  and 
voltmeters)  and  dividing  the  latter  by  the  former. 

These  electrical  methods  of  testing  are  preferable  to 
mechanical  ones,  for  the  reason  that  the  volts  and  amperes 
can  be  easily  and  accurately  measured,  and  their  product 
fives  the  power  in  watts.  Mechanical  measurements  of 
power  by  dynamometer  or  other  means  are  difficult,  and  not, 
usually,  very  accurate. 


Dynamos  and  Motors.  1 1 1 


CHAPTER  XVII. 
MAGNETISM  AND  SEPARATION  OF  LOSSES. 

16.  Magnetism. — Magnetic  measurements  are  difficult  to 
make  with  the  ordinary  apparatus  used  in  practical  work. 
The  proper  method  requires  the  ballistic  galvanometer.  To 
test  the  magnetic  leakage  in  a  dynamo  or  motor,  for  exam- 
ple, a  coil  of  wire  of  any  convenient  size  connected  with  the 
galvanometer  is  put  around  the  field-magnet  and  the  current 
in  the  field  is  stopped,  the  deflection  of  the  galvanometer 
needle  being  noted.  A  coil  of  the  same  number  of  turns  is 
then  put  around  the  armature,  and  the  swing  of  the  galva- 
nometer when  the  field  circuit  is  opened  is  again  noted.  The 
first  deflection  is  to  the  second  as  the  number  of  lines  of 
magnetic  force  in  the  field  is  to  that  in  the  armature,  pro- 
vided the  angles  of  deflection  are  only  a  few  degrees.  If 
the  field  current  is  reversed  the  effects  of  residual  magnetism 
are  eliminated,  and  hence  this  is  better  than  merely  opening 
the  circuit. 

An  ordinary  detector  galvanometer  can  be  used  for  this 
work  if  it  is  not  damped  by  wings  to  prevent  its  swinging 
freely.  A  low-voltage  Weston  voltmeter  or  the  calibration 
coil  of  a  high-reading  one  can  also  be  used  very  conveniently 
for  magnetic  measurements  in  place  of  the  galvanometer.* 
In  a  similar  manner  the  relative  number  of  magnetic  lines 
passing  through  or  leaking  out  of  any  portion  of  the  machine 
may  be  tested  and  the  distribution  of  the  magnetism  deter- 
mined. The  actual  number  of  lines  in  any  magnetic  circuit, 
or  portion  of  circuit,  may  be  determined  either  absolutely 
by  finding  the  constant  of  the  ballistic  galvanometerf  or  by 
comparison  with  a  standard  magnet  having  a  known  number 
of  lines  of  force.  It  may  also  be  calculated  from  the  mag- 
neto-motive force  and  reluctance,;);  or  may  be  measured  by 

*  Paper  by  A.  S.  Ives  in  the  Electrical  World,  Jan.  2,  1892. 

f  Thompson's  "Dynamo-electric  Machinery,"  4th  Ed.,  p.  134. 

\  Thompson's  "  Dynamo-electric  Machinery,"  4th  Ed.,  pp.  406  to  421. 


1 1 2  Practical  Management  of 

an  exploring  coil  of  bismuth,  as  the  resistance  of  this  metal 
is  affected  by  magnetism. 

17.  Separation  of  Losses. — The  total  losses  in  a  dyna- 
mo or  motor,  except  that  caused  by  the  electrical  resistance 
of  the  armature  when  carrying  the  full  current,  can  be  closely 
determined  at  once  by  noting  the  current  required  to  run  it 
free  as  a  motor.  In  a  machine  of  90$  efficiency  this  cannot 
amount  to  more  than  about  8$  of  the  current  required  to 
give  the  full  power.  Consequently  running  free  is  the  easiest 
way  of  testing  a  machine.  The  various  losses  of  power 
which  occur  in  a  dynamo  or  motor  may  be  determined  and 
separated  from  each  other  as  follows: 

Take  a  dynamo,  for  example,  and  drive  it  with  another 
machine  used  as  a  motor  in  the  manner  described  for 
testing  friction  (see  No.  3,  "  Friction  ").  The  motor  should 
be  calibrated  previously — that  is,  tested  to  determine  the 
exact  mechanical  power  it  develops  for  each  amount  of  elec- 
trical power  in  watts  supplied  to  it,  as  described  for  testing 
efficiency  (see  No.  15,  "Efficiency  ").  A  simple  shunt-wound 
motor  on  a  constant-potential  circuit  is  best  suited  to  the 
purpose.  The  dynamo  is  first  driven  at  normal  speed  with 
no  field-magnetism  and  with  the  brushes  lifted  ;  then  the 
actual  power  developed  by  the  motor  (as  shown  by  the  volt- 
meter and  ammeter)  equals  the  power  lost  in  the  dynamo  by 
the  friction  of  the  bearings  and  belt.  The  brushes  are  then 
adjusted  in  contact  with  the  commutator  with  the  usual 
pressure.  The  increase  in  the  power  of  the  motor  (as  shown 
by  the  current  it  then  draws)  is  equal  to  the  brush  friction. 

Finally,  excite  the  field-magnet  to  full  strength,  and  the 
increase  in  the  power  exerted  by  the  motor  is  equal  to  the 
combined  losses  due  to  Foucault  currents  and  hysteresis  in 
the  iron  core  of  the  armature,  provided  there  is  no  consider- 
able magnetic  side  pull  on  the  armature  (see  No.  3,  "  Fric- 
tion ").  The  power  wasted  in  Foucault  currents  varies  as 
the  square  of  the  speed,  while  the  hysteretic  loss  is  only 
directly  proportional  to  speed  ;  hence  the  two  may  be  sepa- 
rated by  testing  the  machine  at  different  speeds. 

For  example,  let  us  call  x  and  y  the  losses  due  to  hyster- 
esis and  Foucault  currents,  respectively,  at  full  speed,  A  the 


Dynamos  and  Motors.  113 

power  consumed  by  both  at  full  speed,  and  B  that  consumed 

*£  Al 

at  half  speed.      Then  A  =  x  +  y  and  B  —  -  +  ^,  and  by 

2        4 

eliminating  JF  we  have/  =  2^4  —  4^.  That  is,  the  Foucault 
loss  is  twice  the  power  consumed  by  both  at  full  speed 
minus  four  times  the  power  lost  by  both  at  half  speed.  The 
hysteresis  loss  =  A  —  y.  If  eddy  currents  are  developed  in 
the  copper  conductors  of  the  armature  they  will  increase  the 
apparent  Foucault  loss  as  determined  by  the  above  test, 
since  they  also  vary  as  the  square  of  the  speed.  The  power 
wasted  by  eddy  currents  might  be  found  by  testing  the 
armature  without  any  conductors  upon  it.  This  could  only 
be  done  before  the  armature  is  wound  or  by  unwinding  it, 
neither  of  which  is  practicable  except  in  the  place  where  it 
is  made.  Ordinarily,  however,  eddy  currents  do  not  amount 
to  much  unless  the  conductors  are  very  large,  and  even  then 
the  use  of  stranded  conductors  or  conductors  embedded  in 
slots  in  the  iron  core  largely  overcomes  the  trouble. 

Friction  of  the  air  might  also  increase  the  apparent  Fou- 
cault loss,  but  it  usually  causes  only  a  very  small  loss  and  is 
almost  impossible  to  separate  except  by  running  the  machine 
in  a  vacuum,  which  is  of  course  impracticable.  The  other 
losses  are  quite  easily  measured  and  separated,  as  follows  : 

The  number  of  watts  used  in  the  field  can  be  measured  by 
a  voltmeter  and  amperemeter,  or  it  can  be  calculated  by  the 

formula   watts  =  ^-  =  C*R  =  EC,  in  which  E  is  E.  M.  F.,  R 
A. 

is  resistance,  and  C  is  the  current.  It  is  sufficient  if  any  two 
of  these  quantities  are  known.  The  loss  in  the  armature 
conductors  due  to  resistance  is  found  by  multiplying  the 
square  of  the  current  in  the  armature  at  full  load  by  the 
armature  resistance;  in  fact,  this  is  usually  called  the  "C*R 
loss."  This  should  not  be  more  than  one  to  three  per  cent 
in  a  constant-potential  dynamo  or  motor,  whether  it  be 
alternating  or  direct  current.  The  sum  of  all  the  losses 
makes  up  the  difference  between  the  total  power  consumed 
by  the  machine  and  the  useful  power  that  it  develops. 

The  ordinary  values  of  the  various  losses  in  a  good 
dynamo  or  motor  of  25  H.  P.  or  more  are  approximately 
as  follows : 


Practical  Management  of 


Useful  power  developed about  90  per  cent 

Used  in  magnetizing  field * 

Loss  in  armature  resistance  (C*R) 

Friction  of  bearings 

"        of  brushes  . 


ar 


Hysteresis  in  armature  core 

Foucault  currents  in  armature  core 


6  2000  4000  GOiOO  8000  10000  12000 

Watts  Output 

ANALYSIS  OF  LOSSES  IN  15  HORSE  POWER  MOTOR  AT  DIFFERENT  LOADS, 
AND  PROPORTION  OF  USEFUL  WORK. 

FIG.  58. 

The  diagram  (Fig.  58)  shows  the  distribution  of  losses 
from  every  cause  in  a  standard  shunt-wound  motor  of  15 


Dynamos  and  Motors.  115 

H.  P.  on  constant-potential  circuit.  As  the  field  strength 
and  speed  are  the  same  at  all  loads,  the  losses  due  to  field 
current,  friction,  and  effects  of  reversal  of  magnetism  in 
armature  core  are  the  same  at  all  times.'  The  armature-cur- 
rent loss,  "  C*R  loss,"  or  loss  due  to  the  resistance  of  the 
armature  winding,  increases  as  the  load  and  current  increase. 
The  power  consumed  (see  scale  at  side  of  diagram),  cor- 
responding to  any  given  power  produced  (scale  at  bottom  of 
diagram),  is  found  by  following  the  straight  line  from  either 
to  the  slanting  line,  and  then  following  at  right  angles  a 
corresponding  line,  to  the  scale  at  the  other  margin.  Or  by 
following  the  line  upward  from  any  given  power  and  com- 
paring itstotal  length,  which  represents  the  power  consumed, 
with  the  length  through  the  white  part,  which  represents 
useful  work.  The  ratio  of  loss  to  useful  work  at  every  load 
can  be  seen  by  following  the  vertical  line  up  from  the  horse- 
power in  question  and  comparing  the  length  through  the 
shaded  part,  representing  loss,  with  the  length  through  the 
white  part,  representing  useful  work.  An  examination  in 
this  way  shows  that  as  the  motor's  load  decreases  from  the 
maximum  the  percentage  of  useful  work  decreases. 


ii6  Practical  Management  of 


PART   III. 

The   Localization   and   Remedy  of  Troubles   in    Dynamos 

or  Motors. 


CHAPTER    XVIII. 
INTRODUCTION. 

THE  promptness  and  ease  with  which  any  accident  or 
difficulty  with  electrical  machinery  may  be  dealt  with, 
whether  by  the  inspector  of  construction  or  by  the  operator 
in  charge  of  running,  will  always  have  much  to  do  with  the 
success  of  the  plant  and  of  those  dependent  upon  it.  It  is 
therefore  likely  that  any  method  to  eliminate  or  reduce  these 
troubles  would  be  very  welcome  to  those  handling  dynamos 
and  motors.  With  the  object  of  obtaining  such  a  method, 
we  have  prepared  a  list  of  troubles,  symptoms,  and  remedies, 
based  upon  quite  an  extensive  experience  with  the  various 
types  and  sizes  of  dynamos  and  motors  in  common  use. 

It  is  evident  that  the  subject  is  somewhat  complicated 
and  difficult  to  handle  in  a  general  way,  since  so  much  de- 
pends upon  the  particular  conditions  in  any  given  case, 
every  one  of  which  must  be  included  in  the  table  in  such  a 
way  as  to  distinguish  it  from  all  others.  Nevertheless,  it  is 
quite  remarkable  how  much  can  be  covered  by  a  systematic 
and  reasonably  simple  statement  of  the  matter,  and  we  feel 
confident  that  nearly  all  of  the  cases  of  trouble  most  likely 
to  occur  are  covered  by  the  table,  and  that  the  detection  and 
remedy  of  the  defect  will  result  from  a  proper  application  of 
the  rules  given. 

It  frequently  happens  that  a  trifling  oversight,  such  as 
allowing  a  wire  to  slip  out  of  a  binding-post,  will  cause  as 
much  annoyance  and  delay  in  the  use  of  electrical  machinery 


Dynamos  and  Motors.  117 

as  the  most  serious  accident.  Other  troubles,  equally  simple 
but  not  as  easily  detected,  are  of  frequent  occurrence.  In 
such  cases  a  very  slight  knowledge  on-  the  part  of  the  man 
having  the  machine  in  charge,  guided  by  a  correct  set  of 
rules,  will  enable  him  to  overcome  the  difficulty  immediately, 
and  save  much  time,  trouble,  and  expense. 

It  must  not  be  supposed  that  this  method  for  treating 
dynamo  and  motor  troubles  is  given  because  these  machines 
are  particularly  liable  to  such  difficulties.  On  the  contrary, 
no  machine  in  existence  is  mechanically  simpler  than  the 
dynamo  or  motor.  The  only  wearing  parts  about  the  ma- 
chine are  the  commutator,  brushes,  and  the  bearings,  all 
of  which  are  made  to  stand  almost  unlimited  use.  In 
this  respect,  therefore,  the  dynamo  or  motor  is  as  simple 
as  an  ordinary  grindstone,  and  infinitely  simpler  than  a 
steam-engine,  which  often  has  a  dozen  or  more  oil-cups 
and  several  dozen  wearing  parts.  Even  a  sewing-machine 
is  far  more  complicated  mechanically  than  any  dynamo  or 
motor.  In  fact,  it  would  be  useless  to  attempt  to  give 
a  method  for  detecting  and  curing  dynamo  and  motor 
troubles  if  it  were  not  for  the  fact  that  these  machines  con- 
sist of  very  few  parts,  which  makes  it  reasonably  possible  to 
locate  the  trouble. 

The  rules  are  made,  as  far  as  possible,  self-explanatory, 
but  a  statement  of  the  general  plan  followed  and  its  most 
important  features  will  facilitate  the  understanding  and  use 
of  the  table. 

USE  OF  THE  TABLE   OF  TROUBLES. 

In  the  use  of  this  table  the  principal  object  should  al- 
ways be  to  separate  clearly  the  various  causes  and  effects 
from  each  other.  A  careful  and  thorough  examination  should 
first  be  made,  and  as  far  as  possible  one  should  be  perfectly 
sure  of  the  facts,  rather  than  attempt  to  guess  what  they  are 
and  jump  at  conclusions.  Of  course  general  precautions  and 
preventive  measures  should  be  taken  before  any  troubles 
occur,  if  possible,  rather  than  wait  until  a  difficulty  has  arisen. 
For  example,  one  should  see  that  the  machine  is  not  over- 
loaded or  running  at  too  high  voltage,  and  should  make  sure 


n8  Practical  Management  of  % 

that  the  oil-cups  are  not  empty.  Neglect  and  carelessness 
with  any  machine  are  usually  and  deservedly  followed  by 
accidents  of  some  sort. 

The  general  plan  of  the  table  is  to  divide  all  troubles 
which  may  occur  to  dynamos  or  motors,  into  nine  classes, 
the  headings  of  which  are  the  nine  most  important  and 
obvious  bad  effects  ever  produced  in  these  machines,  viz. : 

Chap.    XIX.  Sparking  at  Commutator. 

XXI.  Heating  of  Commutator  and  Brushes. 
XXII.  Heating  of  Armature. 

XXIII.  Heating  of  Field-magnets. 

XXIV.  Heating  of  Bearings. 
XXV.  Noise. 

XXVI.  Speed  Too  High  or  Too  Low. 
XXVII.  Motor  Stops  or  Fails  to  Start. 
XXVIII.  Dynamo  Fails  to  Generate. 

Any  one  of  these  general  effects  is  very  evident,  even  to 
the  casual  observer,  and  still  more  so  to  any  person  making 
a  careful  examination,  and  every  one  of  them  is  perfectly 
distinguishable  from  any  of  the  others  without  the  least 
difficulty.  Hence  this  classification  is  perfectly  definite, 
and  makes  it  easy  to  tell,  almost  at  the  first  glance,  under 
which  one  of  these  heads  any  trouble  belongs,  thereby 
eliminating  about  eight  ninths  of  the  possible  cases.  The 
next  step  is  to  find  out  which  particular  one  of  the  eight 
or  ten  causes  in  this  class  is  responsible  for  the  trouble. 
This,  of  course,  requires  more  careful  examination,  but 
nevertheless  can  be  done  with  comparative  ease  in  most 
cases.  Of  course  one  cause  may  produce  two  effects,  and, 
vice  versa,  one  effect  may  be  produced  by  two  causes ;  but 
the  table  is  arranged  to  cover  this  fact  as  far  as  possible. 
In  a  very  complicated  or  difficult  case  it  is  well  to  read 
through  the  entire  table  and  note  what  causes  can  possibly 
apply.  Generally  there  will  not  be  more  than  two  or  three ; 
then  proceed  to  pick  out  the  particular  one  by  following 
the  directions,  which  show  how  each  case  may  be  dis- 
tinguished from  any  other.  Any  dynamo  or  motor  may 


Dynamos  and  Motors.  119 

have  almost  any  of  the  various  troubles,  but  in  each  instance 
the  particular  kind  of  machine  most  liable  to  it  is  specified, 
and  special  directions  are  given  for  special  types.  It  should 
be  remembered  by  those  in  charge,  that  it  is  usually  better 
to  STOP  the  machine  when  any  trouble  manifests  itself,  even 
though  the  difficulty  does  not  seem  to  be  very  serious, 
because  it  is  very  likely  to  develop  into  something  worse. 
There  are,  of  course,  many  cases,  particularly  in  electric- 
lighting,  when  it  is  almost  impossible  to  shut  down.  But 
even  then  spare  machines  should  always  be  ready  to  be 
quickly  substituted  for  the  defective  one.  Of  course,  one 
must  use  his  judgment  and  do  what  is  best  under  the 
circumstances.  The  continued  use  of  faulty  apparatus  is 
too  common,  and  is  often  inexcusable. 

The  table  is  intended  for  the  use  of  those  who  build, 
test,  install,  own,  or  operate  electrical  machinery,  and  all 
statements  apply  equally  well  to  both  dynamos  and  motors, 
unless  otherwise  especially  noted. 


120  Practical  Management  of 


CHAPTER    XIX. 
SPARKING  AT  COMMUTATOR. 

THIS  is  one  of  the  most  common  troubles,  the  objection 
to  it  being  that  it  wears  or  may  even  destroy  the  commu- 
tator and  brushes,  and  produces  heat,  which  may  injure  the 
armature  or  bearings.  Any  machine  having  a  commutator 
is  liable  to  it,  including  practically  all  direct-current  and 
some  alternating-current  machines.  Alternating-current 
machines  have  continuous  collecting  rings  which  are  not 
likely  to  spark,  but  self-exciting  or  compound-wound 
alternators  require  a  supplementary  continuous-current 
commutator  which  may  spark.  This  trouble  can  be  pre- 
vented in  most  cases,  however,  by  proper  construction  and 
care.  Of  all  the  troubles  which  may  occur,  sparking  is  the 
only  one  which  is  very  different  in  the  different  types  of 
machine.  In  some  its  occurrence  is  practically  impossible. 
In  others  it  may  result  from  a  number  of  causes.  The 
following  cases  of  sparking  apply  to  nearly  all  machines, 
and  they  cover  closed-coil  dynamos  and  motors  completely. 

The  very  peculiar  cases  which  may  arise  in  particular 
types  of  open-coil  armatures  can  only  be  reached  by  special 
directions  for  each.  (See  Part  IV.)  A  certain  amount  of 
sparking  occurs  normally  in  most  constant-current  dynamos 
for  arc-lighting,  where  it  is  not  very  objectionable,  since  they 
are  designed  to  stand  it,  and  the  current  is  small. 

I.  Cause. — Armature  carrying  too  much  current,  due  to 
(a)  overload  (for  example,  too  many  lamps  fed  by  dynamo, 
or  too  much  mechanical  work  done  by  constant-potential 
motor) ;  a  bad  short-circuit,  leak,  or  ground  on  the  line  may 
also  have  the  effect  of  overloading  a  dynamo ;  (b)  excessive 
voltage  on  a  constant-potential  circuit  or  excessive  amperes 
on  a  constant-current  circuit.  In  the  case  of  a  motor  on  a 
constant-potential  circuit,  any  friction,  such  as  armature  strik- 
ing pole-pieces,  or  shaft  not  turning  freely,  will  of  course  have 


Dynamos  and  Motors.  121 

the  same  effect  as  overload  in  producing  excessive  current. 
The  armature  of  a  motor  on  a  constant-current  circuit  does 
not  tend  to  heat  more  when  overloaded,  because  the  current 
and  the  heat  it  produces  in  the  armature  (C*  R)  are  constant. 
In  fact  the  armature  can  be  stopped  with  full  current  on 
without  injury  except  loss  of  ventilation. 

Symptom. — Whole  armature  becomes  overheated,  and 
belt  very  tight  on  tension  side,  and  sometimes  squeaks,  due  to 
slipping  on  pulley.  Overload  due  to  friction  is  detected  by 
stopping  machine  and  then  turning  it  slowly  by  hand.  (See 
"  Heating  of  Bearings  "  and  "  Noise,"  Cause  2.) 

Remedy.— (<:)  Reduce  the  load,  or  eliminate  the  short- 
circuit,  leak,  or  ground  on  the  line ;  (d)  decrease  the  size  of 
driving-pulley,  or  (e)  increase  the  size  of  driven  pulley ;  (f) 
decrease  magnetic  strength  of  the  field  in  the  case  of  a 
dynamo  or  increase  it  in  the  case  of  a  motor.  If  excess  of 
current  cannot  satisfactorily  be  overcome  in  any  of  the  above 
ways,  it  will  probably  be  necessary  to  change  the  machine  or 
its  winding.  Overload  due  to  friction  is  eliminated  as 
described  under"  Heating  of  Bearings  "  and  "  Noise,"  Cause 
2,  page  146. 

If  the  starting  or  regulating  box  of  a  motor  on  a  constant 
potential  circuit,  has  too  little  resistance,  it  will  cause  the 
motor  to  start  too  suddenly  and  spark  badly  at  first.  -The 
only  remedy  is  more  resistance  in  the  box. 

2.  Cause. — Brushes  not  set  at  the  neutral  point. 

Symptom. — Sparking  varied  by  shifting  the  brushes 
with  rocker-arm. 

Remedy. — Carefully  shift  brushes  backwards  or  forwards 
until  sparking  is  reduced  to  a  minimum.  This  maybe  done 
by  simply  moving  the  rocker-arm.  If  only  slightly  out  of 
position,  heating  alone  may  result,  without  disarrangement 
being  bad  enough  to  show  sparking.  If  the  brushes  are 
not  exactly  opposite,  or  in  a  four-pole  machine  90°  apart,  they 
should  be  made  so,  the  proper  points  of  contact  being  de- 
termined by  counting  the  commutator-bars  or  measuring 


122 


Practical  Management  of 


with  a  string  or  paper.  The  brushes  should  also  be  care- 
fully adjusted  in  line  with  each  other.  If  one  is  ahead  or 
behind  the  others  they  may  span  too  much  of  the  commu- 
tator. 

The  usual  position  for  brushes  in  two-pole  machines  is 
opposite  the  spaces  between  the  pole-pieces,  but  in  Edison, 
Sprague,  and  some  other  machines  they  must  be  set  at  right 
angles  to  this  position,  and  in  the  T.  H.  motors  about  45°  to 
this  position,  because  the  armature  wires  are  carried  around 
a  portion  of  a  circle  before  reaching  the  commutator.  If 
the  brushes  are  set  very  far  wrong,  namely,  half-way  toward 
the  proper  position  for  the  other  brush,  it  will  cause  a  dyna- 
mo to  fail  to  generate  and  a  motor  to  fail  to  start,  and  in  the 
latter  case  burn  out  or  "  blow"  the  fuse. 

See  "  Dynamo  Fails  to  Generate,"  Cause  6. 

3.  Cause. — Commutator  rough,  eccentric,  or  has  one  or 
more  "  high  bars "  projecting  beyond  the  others,  or  one 
or  more  flat  bars,  commonly  called  "  flats,"  or  projecting 
mica,  any  one  of  which  causes  brush  to  vibrate  or  to  be  ac- 
tually thrown  out  of  contact  with  commutator  (Figs.  59, 


B 


Fui.  59.—  COMMUTATOR  IN  GOOD  CONDITION.     FIG.  60.  —  COMMUTATOR  IN 
BAD  CONDITION.     FIG.  61.  —  HIGH  BAR  ON  COMMUTATOR. 

60,  and  61).  The  effect  of  eccentricity  may  be  produced  by 
the  shaft  being  loose  in  bearings  while  commutator  is  per- 
fectly true  on  shaft.  This  will  allow  whole  armature  to 
chatter  when  running  at  full  speed.  Hard  mica  between 
the  bars  which  does  not  wear  as  rapidly  as  the  copper  will 
throw  brushes  off. 


Dynamos  and  Motors.  123 

Symptom. — Note  whether  there  is  a  glaze  or  polish  on 
the  commutator,  which  shows  smooth  working  ;  touch  revolv- 
ing commutator  with  tip  of  finger-nail  and  K;e  least  rough- 
ness is  perceptible,  or  feel  of  brushes  to  see  if  there  is  any 
jar.  If  the  machine  runs  at  high  voltage  (over  250)  the 
commutator  or  brushes  should  be  touched  with  a  small  stick 
or  quill  to  avoid  danger  of  shock.  In  the  case  of  an  ec- 
centric commutator,  careful  examination  shows  a  rise  and 
fall  of  the  brush  when  commutator  turns  slowly,  or  a 
chattering  of  brush  when  running  fast.  Sometimes  by 
sighting  in  line  with  brush  contact  one  can  see  clear  day- 
light between  commutator  and  brush,  owing  to  brush  jump- 
ing up  and  down. 

Remedy. — Smooth  the  commutator  with  a  fine  file  or 
fine  sand-paper,  which  should  be  applied  by  a  block  of  wood 


FIG.  62. — SLIDE-REST  FOR  TURNING  OFF  COMMUTATOR  WHICH  CLAMPS  ON 
PILLOW-BLOCK  IN  PLACE  OF  ROCKER-ARM. 

which  exactly  fits  the  commutator  (in  latter  case  be  careful 
to  remove  any  sand  remaining  afterward  ;  and  never  use 
emery).  If  bearing  is  loose,  put  in  new  one.  If  commu- 
tator is  very  rough  or  eccentric,  the  armature  should  be 
taken  out  and  put  in  a  lathe,  and  the  commutator  turned 
off.  Large  machines  sometimes  have  a  .slide-rest  attach- 


124  Practical  Management  of 

ment  (Fig.  62),  so  that  the  commutator  can  be  turned  off 
without  removing  the  armature.  This  is  clamped  on  the 
pillow-block  after  removing  the  rocker-arm. 

In  .turning  a  commutator  in  the  lathe,  a  diamond- 
pointed  tool  should  be  used,  this  being  better  than  either  a 
round  or  square  end.  The  tool  should  have  a  very  sharp 
and  smooth  edge,  and  only  an  exceedingly  fine  cut  should 
be  taken  off  each  time  in  order  to  avoid  catching  in  or  tear- 
ing the  copper,  which  is  very  tough.  The  surface  is  then 
finished  by  applying  a  "  dead  smooth  "  file  while  the  commu- 
tator revolves  rapidly  in  the  lathe.  Any  particles  of  copper 
should  then  be  carefully  removed  from  between  the  bars. 

In  order  to  have  the  commutator  wear  smooth  and  work 
well,  it  is  desirable  to  have  the  armature  shaft  move  freely 
back  and  forth  about  a  sixteenth  or  an  eighth  of  an  inch  in 
the  bearings.  The  position  of  the  bearings,  pulley,  collars, 
and  shoulders  on  the  shaft  and  of  the  machine  with  respect 
to  the  belt  should  be  such  as  to  cause  this  to  take  place  of 
itself — except  in  the  case  of  types  of  machines  in  which  the 
pole-pieces  surround  the  ends  of  the  armature  (see  Part  IV). 
It  is  desirable  for  the  commutator  to  have  a  dull  glaze  of  a 
brown  or  bronze  color.  A  very  bright  or  scraped  appear- 
ance does  not  indicate  the  best  condition.  Sometimes 
a  very  little  vaseline  or  a  drop  of  oil  may  be  applied  to  a 
commutator  which  is  rough.  Too  much  oil  is  very  bad,  and 
causes  the  following  trouble. 

4.  Cause. — Brushes  make  poor  contact  with  commutator. 

Symptom. — Close  examination  shows  that  brushes 
touch  only  at  one  corner,  or  only  in  front  or  behind,  or 
there  is  dirt  on  surface  of  contact.  Sometimes,  owing  to 
the  presence  of  too  much  oil  or  from  other  cause,  the 
brushes  and  commutator  become  very  dirty,  and  covered 
with  smut.  They  should  then  be  carefully  cleaned  by 
wiping  with  oily  rag  or  benzine,  or  by  other  means. 

Occasionally  a  "  glass-hard  "  carbon  brush  is  met  with. 
It  is  incapable  of  wearing  to  a  good  seat  or  contact,  and 
will  only  touch  in  one  or  two  points,  and  should  be  dis- 
carded. 

Remedy. — File,  bend,  adjust,  or  clean  brushes  until  they 


Dynamos  and  Motors.  125 

rest  evenly  on  commutator,  with  considerable  surface  of 
contact  and  with  sure  but  light  pressure.  Copper  brushes 
require  a  regular  brush  jig  (Fig.  63).  Carbon  brushes 


FIG.  63. — JIG  FOR  FILING  BRUSHES  TO  THE  CORRECT  BEVEL. 

may  be  fitted  perfectly  by  drawing  a  strip  of  sand-paper 
back  and  forth  between  them  and  the  commutator  while 
they  are  pressing  down,  which  cuts  them  to  the  shape  of 
the  commutator.  A  band  of  sand-paper  may  be  pasted  or 
tied  around  the  commutator,  and  if  the  armature  is  then 
slowly  revolved  by  hand  or  by  power  and  the  brushes  are 
pressed  upon  it,  they  will  be  very  effectively,  rapidly,  and 
perfectly  shaped  to  the  commutator. 

It  sometimes  happens  that  the  brushes  make  poor  con- 
tact, because  the  brush-holders  do  not  turn  or  work  freely. 

5.  Cause. — Short-circuited  coil  in  armature  or  reversed 
coil. 

Symptom. — A  motor  will  draw  excessive  current,  even 
when  running  free  without  load.  A  dynamo  will  require 
considerable  power,  even  without  any  load.  For  reversed 
coil  see  "  Heating  of  armature,"  Cause  6. 

The  short-circuited  coil  is  heated  much  more  than  the 
others,  and  is  very  apt  to  be  burnt  out  entirely ;  therefore 
stop  machine  immediately.  If  necessary  to  run  machine  to 
locate  the  short-circuit,  one  or  two  minutes  is  long  enough, 
but  it  may  be  repeated  until  the  short-circuited  coil  is  found 
by  feeling  the  armature  all  over. 

An  iron  screw-driver  or  other   tool   held  between  the 


126  Practical  Management  of 

field-magnets  near  the  revolving  armature  vibrates  very  per- 
ceptibly as  the  short-circuited  coil  passes.  Almost  any 
armature,  particularly  one  with  teeth,  will  cause  a  slight  but 
rapid  vibration  of  a  piece  of  iron  held  near  it,  but  a  short- 
circuit  produces  a  much  stronger  effect  only  once  per  revolu- 
tion. Be  very  careful  not  to  let  the  piece  of  iron  be  drawn 
in  and  jam  the  armature. 

The  current  pulsates  and  torque  is  unequal  at  different 
parts  of  a  revolution,  these  being  particularly  noticeable  when 
armature  turns  rather  slowly.  If  a  large  portion  of  the  arma- 
ture is  short-circuited  the  heating  is  distributed  and  harder 
to  locate.  In  this  case  a  motor  runs  very  slowly  giving  little 
power,  but  having  full  field-magnetism.  A  short-circuited 
coil  can  also  be  detected  by  the  drop-of-potential  method. 
(For  dynamos,  see  "  Dynamo  Fails  to  Generate,"  Cause  3.) 

Remedy. — A  short  circuit  is  often  caused  by  a  piece  of 
solder  or  other  metal  getting  between  the  commutator-bars 
or  their  connections  with  the  armature,  and  sometimes  the 
insulation  between  or  at  the  ends  of  these  bars  is  bridged 
over  by  a  particle  of  metal.  In  any  such  case  the  trouble 
is  easily  found  and  corrected.  If,  however,  the  short-circuit 
is  in  the  coil  itself,  the  only  real  cure  is  to  rewind  the  coil. 

One  or  more  "grounds"  in  the  armature  may  produce 
effects  similar  to  those  arising  from  a  short-circuit.  (See 
Cause  7.) 

6.  Cause. — Broken  circuit  in  armature. 

Symptom. — Commutator  flashes  violently  while  run- 
ning, and  commutator-bar  nearest  the  break  is  badly  cut  and 
burnt ;  but  in  this  case  no  particular  armature  coil  will  be 
heated,  as  in  the  last  case  (Cause  5),  and  the  flashing  will  be 
very  much  worse,  even  when  turning  slowly.  This  trouble 
which  might  also  be  confounded  with  a  bad  case  of  "  high 
bar*'  or  eccentricity  in  commutator  ("Sparking,"  Cause  3),  is 
distinguished  from  it  by  slowly  turning  the  armature,  when 
violent  flashing  will  continue  if  circuit  is  broken,  but  not  with 
eccentric  commutator  or  even  with  "  high  bar,"  unless  the 
latter  is  very  bad,  in  which  case  it  is  easily  felt  or  seen.  A 


Dynamos  and  Motors. 


127 


very  bad  contact  would  have  almost  the  same  effect  as  a 
break  in  the  circuit. 

Remedy. — A  break  or  bad  contact  may  be  located  by  the 
"  drop"  method  (page  92),  or  by  a  continuity  test  (page  96). 
The  trouble  is  often  found  where  the  armature  wires  connect 
with  the  commutator,  and  not  in  the  coil  itself,  and  the 
break  may  be  repaired  or  the  loose  wire  may  be  resoldered 
or  screwed  back  in  place.  If  the  trouble  is  due  to  a  broken 
commutator  connection,  and  it  cannot  be  fixed,  then  connect 
the  disconnected  bar  to  the  next  by 
solder,  or  "  stagger  "  the  brushes ; 
that  is,  put  one  a  little  forward  and 
the  other  back  so  as  to  bridge  over 
the  break  (Fig.  64).  If  the  break  is 
in  the  coil  itself,  rewinding  js  gen- 
erally the  only  cure.  But  this  may 
be  remedied  temporarily  by  connect- 
ing together  by  wire  or  solder  the 
two  commutator-bars  or  coil  termi- 
nals between  which  the  break  exists. 
It  is  only  in  an  emergency  that 
armature  coils  should  be  cut  out  or  commutator-bars  con- 
nected together,  or  other  makeshifts  resorted  to,  but  it  some- 
times avoids  a  very  undesirable  stoppage.  A  very  rough 
but  quick  and  simple  way  to  connect  two  commutator-bars 
is  to  hammer  or  otherwise  force  the  coppers  together  across 
the  mica  insulation  at  the  end  of  the  commutator.  This 
should  be  avoided  if  possible,  but  if  it  has  to  be  done  in  an 
emergency  it  can  afterwards  be  picked  out  and  smoothed 
over.  In  carrying  out  any  of  these  methods  care  should  be 
taken  not  to  short-circuit  any  other  armature  coil,  which 
would  cause  sparking  (Cause  5). 

7.  Cause. — Ground  in  armature. 

Symptom. — Two  "  grounds  "  (accidental  connections 
between  the  conductors  on  the  armature  and  its  iron  core 
or  the  shaft  or  spider)  would  have  practically  the  same 
effect  as  a  short-circuit  (Cause  5),  and  would  be  treated  in 
the  same  way.  A  single  ground  would  have  little  or  no 


B 


FIG.  64.  —  STAGGERED 
BRUSHES. 


1 28  Practical  Management  of 

effect,  provided  the  circuit  is  not  intentionally  or  accident- 
ally grounded  at  some  other  point.  On  an  electric  railway 
("  trolley  ")  or  other  circuit  which  employs  the  earth  as  the 
return  conductor  one  or  more  grounds  in  the  armature 
would  allow  the  current  to  pass  directly  through  them,  and 
would  cause  the  motor  to  spark  and  have  a  very  variable 
torque  at  different  parts  of  a  revolution. 

Remedy.— A  ground  is  detected  by  testing  with  a  mag- 
neto bell  (page  96).  It  may  be  located  by  the  drop-of- 
potential  method  (page  92).  Another  way  to  locate  it  is  to 
wrap  a  wire  around  the  commutator  so  as  to  make  connec- 
tion with  all  of  the  bars,  and  then  connect  a  source  of 
current  to  this  wire  and  to  the  armature  core  (by  pressing  a 
wire  upon  the  latter).  The  current  will  then  flow  from  the 
armature  conductors  through  the  ground  connection  to  the 
core,  and  the  magnetic  effect  of  the  armature  winding  will 
be  localized  at  the  point  where  the  ground  is.  This  point 
is  then  found  by  the  indications  of  a  compass-needle  when 
slowly  moved  around  the  surface  of  the  armature.  The  cur- 
rent may  be  obtained  from  a  storage-battery  or  from  the 
circuit,  but  then  it  should  be  regulated  by  lamps  or  a  resist- 
ance-box so  as  not  to  exceed  the  normal  armature  current. 
Sometimes  the  ground  may  be  in  a  place  where  it  can  be 
corrected  without  much  trouble,  but  usually  the  particular 
coil  and  often  others  have  to  be  rewound.  A  ground  will 
be  produced  if  the  insulation  is  punctured  by  a  spark  of 
static  electrkity,  which  may  be  generated  by  the  friction  of 
the  belt ;  in  tact,  a  belt  usually  gives  off  electric  sparks  while 
running.  If  the  frame  of  the  machine  is  connected  to  the 
ground  the  static  charge  will  pass  off  to  the  ground,  but 
this  grounding  is  not  generally  considered  allowable.  The 
frame  may  be  connected  to  the  ground  through  a  Geissler 
tube,  a  wet  thread,  a  heavy  pencil-mark  on  a  piece  of  un- 
glazed  porcelain,  or  other  very  high  resistance  which  will 
carry  off  a  static  change  that  is  of  very  high  potential  and 
almost  infinitesimal  quantity,  but  will  not  permit  the  pas- 
sage of  any  considerable  current,  which  might  cause  trouble. 

8.  C  ause. —  Weak  field-magnetism. 


Dynamos  and  Motors.  129 

Symptom. — Pole-pieces  not  strongly  magnetic  when 
tested  with  a  piece  of  iron.  Point  of  least  sparking  is 
shifted  considerably  from  normal  position,  due  to  relatively 
strong  distorting  effect  of  armature  magnetism.  Speed  of  a 
constant-potential  motor  is  usually  high  unless  magnetism 
is  very  weak  or  nil,  in  which  case  a  motor  may  run  slow, 
stop,  or  even  run  backwards.  A  dynamo  fails  to  generate 
the  full  E.  M.  F.  or  current. 

The  particular  cause  of  trouble  may  be  found  as  follows : 
A  broken  circuit  in  the  field  of  a  motor  is  found  by  purposely 
opening  the  field  circuit  at  some  point,  taking  care  to  first 
disconnect  armature  (by  putting  wood  under  the  brushes, 
for  example),  and  to  use  only  one  hand,  to  avoid  shock.  If 
there  is  no  spark  when  circuit  is  thus  opened,  there  must  be 
a  broken  circuit  somewhere.  A  short  circuit  in  the  field- 
coils  is  found  by  measuring  their  resistance  roughly  to  see  if 
it  is  very  much  less  than  it  should  be.  Usually  a  short-cir- 
cuit is  confined  to  one  magnet,  and  will  therefore  weaken 
that  one  more  than  the  others,  and  a  piece  of  iron  held 
half-way  between  the  pole-pieces  will  be  attracted  to  one 
more  than  the  other.  It  may  be  found  by  the  drop-of-poten- 
tial  method  by  testing  from  the  splice  between  the  field- 
coils  to  each  outside  terminal.  "Grounding"  is  practically 
identical  with  short-circuiting,  but  one  ground  will  not  pro- 
duce this  effect  until  another  occurs.  Then  we  have  a 
double  ground,  through  which  the  current  finds  a  complete 
circuit,  which  is  equivalent  to  a  short-circuit.  In  the  ordi- 
nary "trolley"  electric-railway  system  a  ground  return  is 
used,  and  one  ground  may  therefore  be  sufficient  to  cut  out 
one  or  more  field-coils.  This  is,  however,  almost  the  only 
case  in  which  a  grounded  circuit  is  used. 

If  a  field-coil  is  reversed  and  opposed  to  the  others,  it 
will  weaken  the  field-magnetism,  and  cause  bad  sparking. 
This  may  be  detected  by  examining  the  field-coils  to  see  if 
they  are  all  connected  in  the  right  way,  or  by  testing  with  a 
compass  needle.  (See  "  Dynamo  Fails  to  Generate,"  Cause 
4.)  The  series-coil  of  a  compound-wound  dynamo  is  quite 
often  connected  wrongly,  and  will  have  the  effect  of  forcing 
down  the  voltage  the  more  the  load  is  increased  instead  of 
raising  it. 


130  Practical  Management  of 

Remedy. — A  broken  or  a  short  circuit  or  a  ground  is 
easily  repaired  if  it  is  external  or  accessible.  If  it  is  inter- 
nal, the  only  remedy  is  to  replace  or  rewind  the  faulty  coil. 
A  shunt  motor  will  spark  badly  in  starting  if  the  starting- 
box  connects  the  armature  before  the  field.  This  may  be 
remedied  by  adjusting  the  contacts  and  switch-arm.  If  the 
voltage  is  too  low  on  the  circuit,  it  is  likely  to  cause  spark- 
ing in  a  shunt  dynamo  or  motor  ;  and  if  the  voltage  cannot 
be  raised  the  resistance  of  the  field-circuit  should  be  re- 
duced by  unwinding  a  few  layers  of  wire  or  by  substituting 
other  coils. 

(See  "  Speed  Too  High  or  Too  Low,"  "  Motor  Stops  or 
Fails  to  Start,"  "  Dynamo  Fails  to  Generate.") 

9.  Cause. —  Unequal  distribution  of  magnetism.  One  pole- 
tip  very  much  weaker  than  the  other. 

Symptom. — One  brush  sparks  more  than  the  other. 
Remedy. — Reshape  pole-pieces,  or  strengthen  weak  tip. 

10.  Cause. —  Very     high    resistance   brush, — A     carbon 
brush  of   abnormally  high    resistance    may  cause  sparking 
by  being  unable  to    make    good  conducting    contact  with 
commutator.     In   that  case  its  end  will  burn  off  slowly,  as 
with  any  bad  connection. 

Symptom. — Measurement  shows  high  resistance  and  the 
brush  is  very  hot. 

Remedy. — Use  new  brush. 

n.  Cause. —  Vibration  of  machine. 

Symptom. — Considerable  vibration  is  felt  when  the 
hand  is  placed  upon  the  machine,  and  sparking  decreases  if 
the  vibration  is  reduced. 

Remedy. — The  vibration  is  usually  due  to  an  imper- 
fectly balanced  armature  or  pulley  (see  "  Noise,"  Cause  i), 
a  bad  belt  (see  *'  Noise,"  Cause  6),  or  to  unsteady  foundations, 
and  the  remedies  described  for  these  troubles  should  be 
applied. 


Dynamos  and  Motors.  131 

Any  considerable  vibration  is  almost  sure  to  produce 
sparking,  of  which  it  is  a  common  cause.  This  sparking 
may  be  reduced  by  increasing  the  pressure  of  the  brushes 
on  the  commutator,  but  the  vibration  itself  should  be  over- 
come by  the  remedies  referred  to  above. 

12.  Cause. — Chatter  of  brushes. — The  commutator  some- 
times becomes  sticky  when  carbon  brushes  are  used,  causing 
friction,  which  throws  the  brushes  into  rapid  vibration  as  the 
commutator  revolves,  similarly  to  the  action  of  a  violin-bow. 

Symptom. — Slight  tingling  or  jarring  is  felt  in  brushes. 

Remedy. — Clean  commutator  and  oil  slightly.  This 
stops  it  at  once. 

13.  Cause. — Pulsations  of  current,  which  are  common 
in  arc-lighting  circuits,  will  cause  sparking  in  motors  on  such 
circuit. 

Symptom. — An  ammeter  in  the  circuit  will  show  that 
the  current  is  constantly  fluctuating  if  slow ;  if  rapid,  hum- 
ming can  be  heard. 

Remedy. — Steady  the  current  by  better  adjustment  of 
the  regulator  on  the  generator,  or  stop  the  throwing  of 
lamps  or  motors  on  and  off  the  circuit  too  suddenly. 

14.  Cause. — Flying  break  in  armature  conductor. 

Symptom. — No  break  shown  by  test  when  armature 
standing  still,  but  break  shown  when  running  by  flashing  of 
brushes. 

Remedy. — Tighten  connections  to  commutator,  or  re- 
pair broken  wire,  etc. 


132  Practical  Management  of 


CHAPTER   XX. 

HEATING   IN    DYNAMO   OR   MOTOR. 
GENERAL   INSTRUCTIONS. 

THE  degree  of  heat  that  is  injurious  or  objectionable  in 
any  part  of  a  dynamo  or  motor  is  easily  determined  by  feel- 
ing the  various  parts.  If  the  heat  is  bearable  for  a  few  mo- 
ments it  is  entirely  harmless.  But  if  the  heat  is  unbearable 
for  more  than  a  few  seconds  the  safe  limit  of  temperature 
has  been  passed,  except  in  the  case  of  commutators  in  which 
solder  is  not  used ;  and  it  should  be  reduced  in  some  of  the 
ways  that  are  given  below.  In  testing  with  the  hand,  allow- 
ance should  always  be  made  for  the  fact  that  bare  metal 
feels  much  hotter  than  cotton,  etc.  If  the  heat  has  become 
so  great  as  to  produce  an  odor  or  smoke,  the  safe  limit  has 
been  far  exceeded,  and  the  current  should  be  shut  off  and 
the  machine  stopped  immediately,  as  this  indicates  a  serious 
trouble,  such  as  a  short-circuited  coil  or  a  tight  bearing. 
The  machine  should  not  again  be  started  until  the  cause  of 
the  trouble  has  been  found  and  positively  overcome.  Of 
course  neither  water  nor  ice  should  ever  be  used  to  cool 
electrical  machinery,  except  possibly  the  bearings  of  large 
machines,  where  it  can  be  applied  without  danger  df  wetting 
the  other  parts. 

Feeling  for  heat  will  answer  in  ordinary  cases,  but,  of 
course,  the  sensitiveness  of  the  hand  differs,  and  it  makes  a 
very  great  difference  whether  the  surface  is  a  good  or  bad 
conductor  of  heat.  The  back  of  the  hand  is  more  sensitive 
and  less  variable  than  the  palm  for  this  test.  But  for  accu- 
rate results  a  thermometer  should  be  applied  and  covered 
with  waste  or  cloth  to  keep  in  the  heat.  In  proper  work- 
ing the  temperature  of  no  parts  of  the  machine  should  rise 
more  than  45°  C.  or  81°  F.  above  the  temperature  of  the  sur- 
rounding air.  If  the  actual  temperature  of  the  machine  is 
near  the  boiling-point,  100°  C.  or  212°  F.,  it  is  seriously  high. 


Dynamos  and  Motors.  133 

It  is  very  important  in  all.  cases  of  heating  to  locate  cor- 
rectly the  source  of  heat  in  the  exact  part  in  which  it  is  pro- 
duced. It  is  a  common  mistake  to  suppose  that  any  part  of 
a  machine  which  is  found  to  be  hot  is  the  seat  of  the  trouble. 
A  hot  bearing  may  cause  the  armature  or  commutator  to 
heat,  or  vice  versa.  In  every  case  all  parts  of  the  machine 
should  be  felt  to  find  which  is  the  hottest,  since  heat  gener- 
ated in  one  part  is  rapidly  diffused  throughout  the  entire 
machine.  It  is  generally  much  surer  and  easier  in  the  end 
to  make  observations  for  heating  by  starting  with  the  whole 
machine  perfectly  cool,  which  is  done  by  letting  it  stand  for 
one  or  more  hours,  or  over  night,  before  making  the  exami- 
nation. When  ready  to  try  it,  run  it  fast  for  three  to  five 
minutes,  with  the  field-magnets  charged ;  then  stop,  and 
feel  all  parts  immediately.  The  heat  will  be  found  in  the 
right  place,  as  it  will  not  have  had  time  to  diffuse  from  the 
heated  to  the  cool  parts  of  the  machine.  Whereas,  after  the 
machine  has  run  some  time  any  heating  effect  will  spread 
until  all  parts  are  nearly  equal  in  temperature,  and  it  will 
then  be  almost  impossible  to  locate  the  trouble. 

Excessive  heating  of  commutator,  armature,  field-magnets, 
or  bearings  may  occur  in  any  type  of  dynamo  or  motor,  but 
it  can  almost  always  be  avoided  by  proper  care  and  work- 
ing conditions. 


134  Practical  Management  of 


CHAPTER    XXI. 
HEATING  OF   COMMUTATOR   AND   BRUSHES. 

1.  Cause. — Heat  spread  from  another  part  of  machine. 

Symptom. — Start  with  the  machine  cool  and  run  for  a 
short  time,  so  that  heat  will  not  have  time  to  spread.  The 
real  seat  of  trouble  will  then  be  the  part  that  heats  first. 

Remedy.  (See  Heating  of  Armature,  Fields,  or  Bear- 
ings, respectively.) 

2.  Cause. — Sparking. — Any  of  the  causes  of   sparking 
will  cause  heating,  which  may  be  slight  or  serious. 

Symptom  and  Remedy.     (See  "  Sparking.") 

3.  Cause. —  Tendency   to   spark    or   slight  sparking   not 
visible.     Sometimes  before  sparking  appears  serious  heating 
is  produced  by  the   causes  of  sparking,  such  as  the  short- 
circuiting  of  the  coils  as  their  commutator-bars  pass  under 
the  brushes. 

Symptom. — Reduced  by  applying  the  principal  remedies 
for  sparking,  such  as  slightly  shifting  rocker-arm.  Fine 
sparks  may  be  found  by  sighting  in  exact  line  with  the  sur- 
face of  contact  between  the  commutator  and  brushes. 

Remedy.  (See  "  Sparking.") — Apply  the  remedies  with 
extra  care. 

4.  Cause. — Overheated  commutator  will  decompose  carbon 
brush  and  cover  commutator  with  a  black  film,  which  offers 
resistance  and  aggravates  the  heat. 

Symptom. — Commutator  covered  with  dark  coating; 
commutator  brushes  and  holders  show  marks  of  extreme 
heat. 


Dynamos  and 

Remedy. — Clean  off  and  polish  commutator,  reset 
brushes,  start  over  again,  and  watch  carefully. 

5.  Cause. — Bad  connections  in  brush-holder,  cable,  etc. 

Symptom. — Holder,  cable,  etc.,  feels  hottest;  unusual 
resistance  found  in  these  parts  by  "  drop  method,"  p.  92. 

Remedy. — Improve  the  connections. 

6.  Cause. — "Arcing"    or    short-circuit    in    commutator 
across  mica,  or  insulation  between  bars  or  nuts. 

Symptom.— Burnt  spot  between  parts;  spark  appears  in 
the  insulation  when  current  is  put  on. 

Remedy. — Pick  out  the  charred  particles,  take  com- 
mutator apart  and  remedy,  or  put  on  new  commutator. 

7.  Cause. — Carbon  brusJies  heated  by  the  current. 
Carbon    brushes     require    less    attention     than   copper, 

because  they  do  not  cut  the  commutator,  and  their  resist- 
ance prevents  the  development  of  sparking,  but  this  higher 
resistance  causes  them  to  heat  up  more  than  copper  brushes. 

Symptom. — Brushes  hotter  than  other  parts.  Machine 
runs  much  cooler  with  copper  brushes. 

Remedy. — Use  higher  conductivity  carbon.  Let  the 
brush-holder  grip  brush  closer  to  commutator  so  as  to  reduce 
the  length  of  brush  through  which  the  current  has  to  pass. 
Reinforce  the  brush  with  copper  gauze,  sheet  copper,  or 
wires  run  through  it,  or  use  some  form  of  the  combined 
metal  and  carbon  brushes  that  are  on  the  market.  Use 
larger  brushes  or  a  greater  number  of  them. 


136  Practical  Management  of 


CHAPTER   XXII. 
HEATING   OF   ARMATURE. 

NOTE. — Any  excess  of  current  taken  by  an  armature  when  running  FREE, 
whatever  the  cause,  must  be  converted  into  heat  by  some  defect  in  the 
motor,  hence  the  "free  current"  is  the  simplest  and  most  complete  test  of 
the  efficiency  and  perfect  condition  of  a  machine. 

1 .  Cause. — Excessive  current  in  armature  coils. — Symptom 
and  Remedy  the  same  as  "  Sparking,"  Cause  I. 

2.  Cause. — Short-circuited  armature  coils. — Symptom  and 
Remedy  the  same  as  "  Sparking,"  Cause  5.    See  also  Cause  7. 

3.  Cause. — Moisture  in  armature  coils. 

Symptom. — Armature  requires  considerable  power  to 
run  free.  Armature  steams  when  hot,  or  feels  moist.  This 
is  really  a  special  case  of  Cause  2,  as  moisture  has  the  effect 
of  short-circuiting  the  coils  through  the  insulation.  Measure 
insulation  of  armature,  which  would  be  much  lowered  by 
moisture. 

Remedy. — Bake  the  armature  for  five  hours  in  an  oven 
or  other  place  which  is  sufficiently  warm  to  drive  out  the 
moisture,  but  not  hot  enough  to  run  any  risk  of  burning  or 
even  slightly  charring  the  insulation.  A  very  neat  way  to 
do  this  is  to  pass  a  current  through  the  armature,  which 
should  be  regulated  so  as  to  be  about  three  quarters  of  the 
full  armature  current,  the  armature  being  held  still  and 
turned  over  only  once  or  twice  to  prevent  the  shellac  run- 
ning to  one  side  when  hot.  If  weather  is  damp  armature 
should  be  baked  all  day  or  all  night,  and  in  any  case  until  its 
insulation  measures  at  least  I  megohm. 

4.  Cause. — Foucault  currents  in  armature  core. 

Symptom. — Iron  of  armature  core  hotter  than  coils  after 
a  short  run,  and  considerable  power  required  to  run  armature 
when  field  is  magnetized  and  there  is  no  load  on  armature. 
This  may  be  distinguished  from  Cause  2,  by  absence  of  spark- 


Dynamos  and  Motors.  137 

ing  and  absence  of  excessive  heat  in  a  particular  coil  or  coils 
after  a  short  run.    (See  Part  II,  17,  "  Separation  of  Losses.") 

Remedy. — Armature  core  should  be  laminated  more 
perfectly,  which  is  a  matter  of  first  construction. 

5.  Cause. — Eddy  currents  in  armature  conductors. 

Symptom. — The  same  as  Cause  4,  except  that  armature 
conductors  are  hotter  than  core  even  without  any  load. 

Remedy. — This  trouble  is  due  to  one  side  of  each  arma- 
ture conductor  having  E.  M.  F.  generated  in  it  before  the 
other  side;  it  is,  therefore,  found  in  machines  with  large 
armature  conductors  or  bars.  It  is  overcome  by  reducing 
the  thickness  of  the  conductors  or  by  splitting  them  up  into 
a  number  of  strips  or  strands,  which  should  be  twisted  to 
equalize  them.  Rounding  or  bevelling  off  the  edges  of  the 
pole  pieces  will  also  reduce  the  trouble,  as  will  also  sinking 
the  conductors  in  slots  in  the  armature  core.  Fig.  72*2.  (See 
Part  II,  17,  "Separation  of  Losses.") 

6.  Cause. — One  or    more  reversed  coils   on   one  side  of 
armature,    which    will    cause   a   local    current    to    circulate 
around  armature. 

Symptom. — Excessive  current  when  running  free,  but 
no  coil  heated  more  than  others.  If  current  is  applied  to 
each  coil  in  succession  by  touching  wires  carrying  current  to 
each  two  adjacent  commutator  bars,  a  compass  needle  held 
over  the  coils  will  behave  differently  when  the  reversed  coil 
is  reached.  In  a  motor  the  half  of  armature  containing  the 
reversed  coils  is  heated  more  than  the  other. 

Remedy. — Reconnect  the  coil  to  agree  with  the  others. 

7.  Cause. — Heat  conveyed  from  other  parts. 
Symptom. — Other  parts  hotter  than  armature.       Start 

with  machine  cool  and  see  if  other  parts  heat  first.  . 

Remedy.  (See  Heating  of  Bearings,  Field,  Commutator, 
etc.,  as  the  case  may  be.) 

8.  Cause. — Flying  cross  in  armature  conductor. 
Symptom  and  Remedy. — Similar  to  sparking  (Cause  14), 

except  that  it  refers  to  the  insulation  of  the  conductors. 


138  Practical  Management  of 


CHAPTER  XXIII. 

HEATING   OF   FIELD-MAGNETS. 

1.  Cause. — Excessive  current  in  field  circuit. 
Symptom. — Field-coils  too  hot  to  keep  the  hand  on. 

Remedy. — In  the  case  of  a  shunt-wound  machine  de- 
crease the  voltage  at  terminals  of  field-coils,  or  increase  the 
resistance  in  field  circuit  by  winding  on  more  wire  or  putting 
resistance  in  series.  In  the  case  of  a  series-wound  machine, 
shunt  a  portion  of,  or  otherwise  decrease,  the  current  passing 
through  field,  or  take  a  layer  or  more  of  wire  off  the  field- 
coils,  or  rewind  with  coarser  wire.  This  trouble  might  be 
due  to  a  short-circuit  in  field-coils  in  the  case  of  a  shunt- 
wound  dynamo  or  motor,  and  would  be  indicated  by  one 
pole-piece  with  the  short-circuited  coil  being  weaker  than  the 
other  ;  one  of  the  coils  would  also  probably  be  hotter  than 
the  other  ;  but  this  can  only  be  remedied  by  rewinding 
short-circuited  coil.  Measure  resistance  of  field  coils  to  see 
if  they  are  nearly  equal.  (See  "  drop  method,"  page  92.) 
If  the  difference  is  considerable  (i.e.,  more  than  5  or  10  per 
cent),  it  is  almost  a  sure  sign  that  one  coil  is  short-circuited 
or  double-grounded.  If  one  field  coil  is  muck  hotter  than  tJie 
other,  the  trouble  probably  lies  in  the  cooler  coil,  as  it  is  short- 
circuited  and  allows  the  other  to  carry  excessive  current  and 
become  heated. 

2.  Cause. — Foucault  currents  in  pole-pieces. 

Symptom. — The  pole-pieces  hotter  than  the  coils  after 
a  short  run.  When  making  the  comparison  it  is  necessary 
to  keep  the  hand  on  the  coils  some  time  before  the  full 
effect  is  reached,  because  the  coils  are  insulated  and  the 
pole-pieces  are  bare  metal,  and  even  then  the  coils  will  not 
feel  so  hot,  although  their  actual  temperature  may  be  higher 
if  measured  by  a  thermometer. 


Dynamos  and  Motors.  139 

Remedy. — -This  trouble  is  either  due  to  faulty  design 
and  construction,  which  can  only  be  corrected  by  rebuilding, 
or  else  it  is  caused  by  fluctuations  in  the  current.  The  latter 
can  be  detected  if  the  variations  are  not  too  rapid,  by  put- 
ting an  ammeter  in  circuit,  or  rapid  variations  may  be  felt 
by  holding  a  piece  of  iron  near  the  pole-pieces  and  noting 
whether  it  vibrates.  In  the  case  of  an  alternating  current 
it  is  necessary  to  use  laminated  fields  to  avoid  great 
heating,  and  the  ordinary  arc  currents  fluctuate  en6ugh 
to  cause  some  trouble  in  this  way.  In  fact,  the  currents 
generated  by  the  open-coil  armatures  used  in  arc-lighting 
(Thomson-Houston  and  Brush,  for  example)*  are  pulsating 
in  character,  and  are  apt  to  cause  Foucault  currents  and 
heating  in  the  field-magnets  of  motors  fed  by  such  currents. 

3.  Cause. — Moisture  in  field-coils. 

Symptom. — Field-circuit  tests  lower  in  resistance  than 
normal  in  that  type  of  machine,  and  in  the  case  of  shunt- 
wound  machines  the  field  takes  more  than  the  ordinary  cur- 
rent. Field-coils  steam  when  hot,  or  feel  moist  to  hand. 
The  insulation  resistance  also  tests  low. 

Remedy. — The  same  as  for  moisture  in  armature,  page 
136. 

*  A  Study  of  an  Open-coil  Arc  Dynamo,  by  M.  E.  Thompson,  Electrical 
Engineer,  May27,i89i. 


140  Practical  Management  of 


CHAPTER  XXIV. 
HEATING  OF   BEARINGS. 

THIS  may  arise  in  any  machine.  The  cause  should  be 
found  and  removed  promptly,  but  heating  of  the  bearings 
may  be  reduced  temporarily  by  applying  cold  water  or  ice 
to  them.  This  is  only  allowable  when  it  is  absolutely  nec- 
essary to  keep  running,  and  great  care  should  be  taken  not 
to  allow  any  water  to  get  upon  the  commutator,  armature, 
or  field-coils,  as  it  might  short-circuit  or  ground  them.  If 
the  bearing  is  very  hot,  the  shaft  should  be  kept  revolving 
slowly,  as  it  might  "  freeze"  or  stick  fast  if  stopped  entirely. 

1.  Cause. — Lack  of  oil. 

Symptom. — Oil  cup  or  reservoir  empty.  Oil  passages 
clogged.  Self-oiling  rings  stuck  fast.  Shaft  and  bearing 
look  dry.  The  shaft  does  not  turn  freely. 

Remedy. — Supply  oil,  and  make  sure  that  oil  passages  as 
well  as  feeding  or  self-oiling  devices  work  freely,  and  that 
the  oil  cannot  leak  out.  This  last  fault  sometimes  causes 
oil  to  fail  sooner  than  attendant  expects.  Good  quality  of 
oil  should  always  be  used,  as  poor  oil  might  be  as  bad  as  no 
oil. 

2.  Cause. — Grit  or  other  foreign  matter  in  bearings. 

Symptom. — Best  detected  by  removing  shaft  or  bearing 
and  examining  both.  Any  grit  can  of  course  be  felt  easily, 
and  will  also  scratch  the  shaft. 

Remedy. — Remove  shaft  or  bearing,  clean  both  very 
carefully,  and  see  that  no  grit  can  get  in.  Place  machine  in 
dustless  place  or  box  it  in.  The  oil  should  be  perfectly 
clean  ;  if  not,  it  should  be  filtered.  If  it  is  not  possible  to 
stop  the  machine  or  to  remove  the  shaft  the  dirt  might  be 


Dynamos  and  Motors.  14 1 

washed  out  with  kerosene  or  water,  but  these  should  not  be 
allowed  to  get  on  the  commutator, 
armature,  or  field-coils. 

3.  Cause. — Shaft  rough  or  cut. 

CFicr    6n  ">  FlG-  65- — SHAFT  ROUGH  OR 

eat. 

Symptom.  —  Shaft   will    show 
grooves  or  roughness,  and  will  probably  revolve  stiffly. 

Remedy. — Turn  shaft  in  lathe  or  smooth  with  fine  file, 
and  see  that  bearing  is  smooth  and  fits  shaft. 

4.  Cause. — Shaft  and  bearing  fit  too  tight. 
Symptom. — Shaft  hard  to  revolve  by  hand. 

Remedy. — Turn  or  file  down  shaft  in  lathe,  or  scrape  or 
ream  out  bearings. 

5.  Cause. — Shaft  "sprung"  or  bent. 

Symptom. — Shaft  hard  to  revolve,  and  usually  sticks 
much  more  in  one  part  of  revolution  than  in  another. 

Remedy. — It  is  almost  impossible  to  straighten  a  bent 
shaft.  It  might  be  bent  back  or  turned  true,  but  probably 
a  new  shaft  will  be  necessary. 

6.  Cause. — Bearings  out  of  line. 

Symptom. — Shaft  hard  to  revolve,  but  is  much  relieved 
by  slightly  loosening  the  screws  which  hold  bearings  in 
place.  "  Bearing  sometimes  moves  perceptibly  when  loos- 
ened. This  should  be  tried,  however,  when  the  motor  is 
not  running  and  the  belt  is  off. 

Remedy. — Loosen  the  bearings  by  partly  unscrewing 
bolts  or  screws  holding  them  in  place,  and  find  their  easy 
and  true  position,  which  may  require  one  of  them  to  be 
moved  either  sideways  or  up  and  down  ;  then  file  the  screw- 
holes  of  that  bearing  or  raise  or  lower  it,  as  may  be  neces- 
sary, to  make  it  occupy  the  right  position  when  the  screws 
are  tightened.  The  armature  must  be  kept,  however,  in  the 
centre  of  the  space  between  the  pole-pieces,  so  that  the 
clearance  is  uniform  all  around.  (See  Cause  9.) 


I42 


Practical  Management  of 


7.  Cause. —  Thrust  or  pressure  of  pulley ,  collar ,  or  shoul- 
der on  shaft  against  one  or  both  of  the  bearings.  (Figs.  66 
and  67.) 


FIG.  66. — ARMATURE  WITH  GOOD  CLEARANCE  AT  C.C. 


FIG.  67. — ARMATURE  FORCED  AGAINST  BEARING. 

Symptom. — Move  shaft  back  and  forth  with  the  finger 
or  a  stick  applied  to  the  end  while  revolving,  and  note  if  the 
collar  or  shoulder  tends  to  be  pushed  or  drawn  against 
either  bearing.  A  dynamo  or  motor  shaft  should  usually  be 
capable  of  moving  freely  back  and  forth  a  sixteenth  or  an 
eighth  of  an  inch  to  make  commutator  and  bearings  wear 


Dynamos  and  MqjoKp      RSITY  1       ,  ^ 


smooth,  except  in  machines  in  which  'tKe^poTe-pieces  sur- 
round the  ends  of  the  armature.  (See  Remedy  "  Sparking," 
Cause  3.)  This  trouble  may  be  relieved  in  one  of  the  follow- 
ing ways  : 

Remedy. — Line  up  the  belt,  shift  collar  or  pulley,  turn 
off  shoulder  on  shaft  or  file  off  bearing  until  'the  shoulder 
does  not  touch  when  running  or  until  pressure  is  relieved. 

8.  Cause. — Too  great  load  or  strain  on  the  belt. 

Symptom. — Great  tension  on  belt.  In  this  case  pulley 
bearing  will  probably  be  very  much  hotter  than  the  other, 
and  also  worn  elliptical,  as  indicated  in 
Fig.  68,  in  which  case  the  shaft  may  be 
shaken  in  the  bearing  in  the  direction 
of  the  belt  pull,  when  the  belt  is  off, 
provided  the  machine  has  been  running 
long  enough  to  wear  the  bearings. 

Remedy. — Reduce  load  or  belt  ten- 
sion, or  use  larger  pulleys  and  lighter 
belt,  so  as  to  relieve  si'de  strain  on  shaft. 
(See  "  Belting,"  Chapter  IV.) 

~  FIG.  68. — BEARING  WORN 

9.  Cause. — Armature  too  near  one  ELLIPTICAL. 

pole-piece,  producing  much  greater  mag- 
netic attraction  on  nearer  side. 

Symptom. — Examine  the  clearance  of  armature,  and  see 
if  it  is  uniform  on  all  sides.  Charge  and  discharge  the  field- 
magnet,  the  armature  being  disconnected  (by  putting  wood 
under  one  set  of  brushes),  and  see  if  armature  seems  to  be 
drawn  to  one  side  and  turns  very  much  less  easily  when  field 
is  magnetized. 

Remedy. — This  fault  is  either  due  to  a  defect  in  the 
original  construction,  or  to  wear  in  the  bearings,  either  of 
which  is  difficult  to  correct ;  but  in  cases  of  necessity  the 
armature  can  be  centred  exactly  in  the  field  by  moving 
the  bearings,  which  may  be  done  by  carefully  filing  the  holes 
through  which  the  screws  pass  that  hold  the  bearings  in 
place,  or  the  pole-piece  may  be  filed  away  where  it  is  too 
near  the  armature.  In  small  machines  it  is  sometimes  pos- 


144  Practical  Management  of 

sible  to  spring  the  pole-piece  farther  away  from  the  arma- 
ture, but  this  is  difficult  and  dangerous  to  attempt.  Trouble 
from  this  cause  is  greater  in  multipolar  than  in  bipolar  ma- 
chines ;  therefore  the  clearance  between  the  armature  and 
pole  pieces  should  be  larger  in  the  former  than  in  the  latter, 
and  the  former  are  sometimes  provided  with  screws  for 
shifting  the  fields.  This  difficulty  always  tends  to  become 
aggravated,  because  the  more  the  side  pull  the  more  the 
bearings  wear  in  that  direction.  If,  on  the  other  hand,  the 
armature  is  in  the  centre  of  the  space  formed  by  the  pole- 
pieces,  the  magnetic  pull  is  practically  balanced  in  all  direc- 
tions-. 

It  is  risky  to  file  bolt  holes  or  make  any  such  change 
in  a  machine,  and  it  should  never  be  attempted  before  con- 
sulting an  experienced  machinist.  Very  often  the  trouble  is 
due  to  the  parts  being  out  of  place  merely  because  they 
have  not  been  put  together  right  or  there  is  dirt  between 
them.  If  the  bearing  is  warm  or  the  shaft  out  of  centre, 
the  former  may  be  rebabbittecl  or  renewed. 

10.  Cause. — Bearing  heated  by  hot  pulley,  commutator, 
or  armature. 

Symptom. — Pulley,  armature,  or  commutator  hotter  than 
bearing.  The  slipping  of  the  belt  on  the  pulley,  sparking 
at  the  commutator,  or  heating  of  the  armature  may  heat  one 
or  both  bearings  of  the  machine,  in  which  case  an  examina- 
tion will  show  that  these  parts  are  hotter  than  the  bearing, 
and  are  the  real  source  of  the  trouble. 

Remedy.— A  slipping  belt,  sparking  commutator,  or  hot 
armature  can  be  cured  as  described  under  these  headings, 
and  then  the  bearing  will  probably  cease  to  heat. 


Dynamos  and  Motors. 


CHAPTER   XXV. 

NOISE. 

I.  Cause. —  Vibration  due  to  armature  or  pulley  being  out 
of  balance. 

Symptom. — Strong  vibration  felt  when  the  hand  is  placed 
upon  the  machine  while  it  is  running.  Vibration  changes 
greatly  if  speed  is  changed,  and  sometimes  almost  disappears 
at  certain  speeds. 

Remedy. — Armature  or  pulley  must  be  perfectly  bal- 
anced by  securely  attaching  lead  or  other  weight  on  the 
light  side,  or  by  drilling  or  filing  away  some  of  the  metal  on 
the  heavy  side.  The  easiest  method  of  finding  in  which 
direction  the  armature  is  out  of  balance  is  to  take  it  out  and 
rest  the  shaft  on  two  parallel  and  horizontal  A-shaped 
metallic  tracks  sufficiently  far  apart  to  allow  the  armature 


FIG.  69. — METHOD  OF  BALANCING  ARMATURE. 

to  go  between  them  (Fig.  69).  If  the  armature  is  then 
slowly  rolled  back  and  forth,  the  heavy  side  will  tend  to 
turn  downward.  The  armature  and  pulley  should  always  be 
balanced  separately.  An  excess  of  weight  on  one  side  of  the 
pulley  and  an  equal  excess  of  weight  on  the  opposite  side 
of  the  armature  will  not  produce  a  balance  while  running, 
though  it  does  when  standing  still ;  on  the  contrary,  it  will 


146  Practical  Management  of 

give  the  shaft  a  strong  tendency  to  "  wobble."  A  perfect 
balance  is  only  obtained  when  the  weights  are  directly 
opposite,  i.e.,  in  the  same  line  perpendicular  to  the  shaft. 

2.  Cause. — Armature  strikes  or  rubs  against  pole-pieces. 

Symptom. — Easily  detected  by  placing  the  ear  near  the 
pole-pieces  or  by  examining  armature  to  see  if  its  surface  is 
abraded  at  any  point,  or  by  examining  each  part  of  the 
space  between  armature  and  field,  as  armature  is  slowly 
revolved,  to  see  if  any  portion  of  it  touches  or  is  so  close  as 
to  be  likely  to  touch  when  the  machine  is  running.  Or  turn 
armature  by  hand  when  no  current  is  on,  and  note  if  it 
sticks  at  any  point.  It  is  unwise  to  have  a  clearance  of  less 
than  -J-  to  J  inch. 

Remedy. — Bind  down  any  wire  or  other  part  of  the 
armature  that  may  project  abnormally,  or  file  out  the  pole- 
pieces  where  the  armature  strikes,  or  centre  the  armature  so 
that  there  is  a  uniform  clearance  between  it  and  the  pole- 
pieces  at  all  points. 

3.  Cause. — Shaft  collar  or  shoulder,  hub  or  edge  of  pulley, 
or  belt  strikes  or  scrapes  against  bearings. 

Symptom. — Rattling  noise,  which  stops  when  the  shaft 
or  pulley  is  pushed  lengthwise  away  from  one  or  the  other 
of  the  bearings.  (See  "  Heating  of  the  Bearings,"  Cause  7.) 

Remedy. — Shift  the  collar  or  pulley,  turn  off  the 
shoulder  on  the  shaft,  file  or  turn  off  the  bearing,  move 
the  pulley  on  the  shaft  or  straighten  the  belt  until  there  is 
no  more  striking  and  noise  ceases. 

4.  Cause. — Rattling  due  to  looseness  of  screws  or  other 
parts. 

Symptom. — Close  examination  of  the  bearings,  shaft, 
pulley,  screws,  nuts,  binding-posts,  etc.,  or  touching  the 
machine  while  running,  or  shaking  its  parts  while  standing 
still,  shows  that  some  parts  are  loose.  • 

Remedy. — Tighten  up  the  loose  parts,  and  be  careful  to 
keep  them  all  in  place  and  properly  set  up.  It  is  very  easy 


Dynamos  and  Motors.  147 

to  guard  against  the  occurrence  of  this  trouble,  which  is 
very  common,  by  simply  examining  the  various  screws  and 
other  parts  each  day  before  the  machine  is  started.  Elec- 
trical machinery  being  usually  high  speed,  the  parts  are 
particularly  liable  to  shake  loose.  A  worn  or  poorly  fitted 
bearing  might  allow  the  shaft  to  rattle  and  make  a  noise,  in 
which  case  the  bearing  should  be  refitted  or  renewed. 

5.  Cause. — Singing  or  hissing  of  brushes. — This  is  usu- 
ally occasioned  by  rough  or  sticky  commutator  (see  "  Spark- 
ing," Causes  3  and  12),  or  by  tips  of  brushes  not  being 
smooth,  or  the  layers  of  a  copper  brush  not  being  held 
together  and  in  place.  With  carbon  brushes,  hissing  will  be 
caused  by  the  use  of  carbon  which  is  gritty  or  too  hard. 
Vertical  carbon  brushes  or  brushes  inclined  against  the 
direction  of  rotation  are  apt  to  squeak  or  sing.  A  new 
machine  will  sometimes  make  noise  from  rough  commu- 
tator, no  matter  how  carefully  it  is  turned  off,  because  the 
difference  in  hardness  between  mica  and  copper  causes  the 
cut  of  the  tool  to  vary,  thus  forming  inequalities  which  are 
very  minute,  but  enough  to  make  noise.  This  can  best  be 
smoothed  by  running. 

Symptom. — Sound  of  high  pitch,  and  easily  located  by 
placing  the  ear  near  the  commutator  while  it  is  running,  and 
by  lifting  off  the  brushes  one  at  a  time,  provided  there  are 
two  or  more  on  each  side,  so  that  the  circuit  is  not  opened. 
If  there  is  no  current,  there  is  no  objection  to  raising  the 
brushes. 

Remedy. — Apply  a  very  little  oil  or  vaseline  to  the  com- 
mutator with  the  finger  or  a  rag.  Adjust  the  brushes  or 
smooth  the  commutator  by  turning,  filing,  or  fine  sand-paper, 
being  careful  to  clean  thoroughly  afterwards.  Carbon 
brushes  are  apt  to  squeak  in  starting  up  or  at  slow  speed. 
This  decreases  at  full  speed,  and  can  usually  be  reduced  by 
moistening  the  brush  with  oil,  care  being  taken  not  to  have 
any  drops  or  excess  of  oil.  Shortening  or  lengthening  the 
brushes  sometimes  stops  the  noise.  Run  the  machine  on 
open  circuit  until  commutator  and  brushes  are  worn  smooth. 


148 


Practical  Management  of 


Cause.  —  Flapping  or  pounding  of  belt  joint  or  lacing 
against  pulley.  (Fig.  70.) 

Symptom.  —  Sound  repeated  once  for  each  complete 
revolution  of  the  belt,  which  is  much  less  frequent  than 
any  other  dynamo  or  motor  sound,  and  can  be  easily  de- 
tected or  counted. 


FIG.  70. — BAD  JOINTS  IN  BELT. 

Remedy. — Endless  belt  or  smoother  joint  in  belt.  A  per- 
fect joint  and  a  straight,  smooth  belt  are  always  very  desir- 
able for  dynamos  and  motors.  (See  "  Belting,"  Chapter  IV. 

7.  Cause. — Slipping  of  belt  on  pulley  due  to  overload. 
Symptom. — Intermittent  squeaking  noise. 

Remedy. — Tighten  the  belt  or  reduce  the  load.  A  wider 
belt  or  larger  pulley  may  be  required.  Powdered  rosin 
may  be  put  on  the  belt  to  increase  its  adhesion  ;  but  it  is  a 
makeshift,  injurious  to  the  belt,  only  to  be  adopted  if  neces- 
sary. (See  "  Belting,"  Chapter  IV.) 

8.  Cause. — Humming  of  armature-core  teeth  (if  any)  as 
they  pass  pole-pieces. 

Symptom. — Pure  humming  sound  less  metallic  than 
Cause  5. 

Remedy. — Slope  or  chamfer  the  ends  of  the  pole-pieces 
so  that  each  armature  tooth  does  not  pass  the  edge  of  the 
pole-piece  all  at  once.  Decrease  the  magnetization  of  the 
fields.  Increase  the  cross-section  or  magnetic  capacity  of 
the  teeth,  or  reduce  that  of  the  body  of  the  armature.  But 
these  are  nearly  all  matters  of  first  construction,  and  are 
made  right  by  good  manufacturers. 

9.  Cause. — Humming  due   to   alternating  or  pulsating 
current. 

Symptom. — This  gives  a  sound  similar  to  that  in  the 
preceding  case,  but  louder.  The  two  troubles  can  be  distin- 


Dynamos  and  Motors. 


149 


guished,  if  necessary,  by  determining  whether  the  note  given 
out  corresponds  to  the  number  of  alternations,  or  to  the 
number  of  armature  teeth  of  generator  passing  per  second. 
Usually  the  latter  is  considerably  greater  than  the  former. 
This  trouble  is  confined  to  alternating-current  apparatus,  and 
to  motors  on  circuits  operated  by  some  forms  of  dynamos 
having  commutators  with  few  segments,  or  having  toothed 
armatures.  (See  "  Heating  of  Field  Magnets,"  Cause  2.) 

Remedy. — It  is  practically  inherent  in  alternating  appa- 
ratus, but  its  effects  can  be  reduced  by  mounting  the  machine 
on  rubber,  or  otherwise  deadening  the  sound. 


FIG.  71. — DIRECT-CONNECTED  GENERATORS. 

Note. — It  often  happens  that  a  dynamo  or  motor  seems 
to  make  a  noise,  which  in  reality  is  caused  by  the  engine  or 
other  machine  with  which  it  is  coupled  (Fig.  71),  or  by  other 
connections  that  may  be  used.  Very  careful  listening  with 
the  ear  close  to  the  different  parts  will  show  exactly  where 
the  noise  originates.  A  very  sensitive  way  to  locate  a  noise 
or  vibration  is  to  hold  a  short  stick  or  pencil  by  one  end  be- 
tween the  teeth  and  press  the  other  end  squarely  against  the 
several  parts,  to  ascertain  which  particular  one  gives  the 
greatest  vibration. 


150  Practical  Management  of 


CHAPTER  XXVI. 
SPEED  TOO   HIGH  OR  TOO   LOW. 

THIS  is  generally  a  serious  matter  in  either  dynamo  or 
motor,  and  it  is  always  desirable  and  often  imperative  to  shut 
off  the  power  or  current  immediately,  and  make  a  careful 
investigation  of  the  trouble. 

SPEED   TOO   LOW. 

1.  Cause. — Overload.     (See  "  Sparking,"  Cause  I.) 

Symptom. — Armature  runs  more  slowly  than  usual.  Bad 
sparking  at  commutator.  Ammeter  indicates  excessive  cur- 
rent. Armature  and  bearings  heat.  Belt  very^tight  on 
tension  side. 

Remedy. — Reduce  the  load  on  machine  by  taking  off 
lamps  in  the  case  of  a  dynamo,  or  mechanical  work  in  the 
case  of  a  motor;  decrease  the  diameter  of  driving  pulley  or 
increase  the  diameter  of  driven  pulley.  If  necessary  to 
relieve  strain  of  overload  temporarily  decrease  the  E.  M.  F. 
on  either  a  dynamo  or  motor. 

2.  Cause. — Short-circuit  or  ground  in  armature. 

Symptom  and  Remedy  the  same  as  "  Heating  of  Arma- 
ture." (Cause  2  and  Cause  7.) 

3 .  C  au  se. — A  rmatu re  strikes  pole-pieces. 

Symptom  and  Remedy  the  same  as  "  Noise,"  Cause  2. 

4.  Cause. — Shaft  does  not  revolve  freely  in  the  bearings. 

Symptom. — Armature  turns  hard  by  hand  ;  bearings 
and  shaft  heat  when  running. 

Remedy. — Oil  the  bearings  ;  clean  and  smooth,  if  nec.es- 
sary,  the  shaft  and'  bearings  ;  line  up  the  bearings.  (See 
"  Heating  of  Bearings,"  all  cases). 


Dynamos  and  Motors.  151 

SPEED   HIGH   OR  LOW. 

5.  Cause. — Field-magnetism  weak. 

This  has  the  effect,  on  a  constant-voltage  circuit,  of  mak- 
ing a  motor  run  too  fast  if  lightly  loaded,  or  too  slow  if 
heavily  loaded,  or  even  run  backwards  if  the  field-magnet  is 
not  excited  at  all,  as,  for.  example,  when  the  field  circuit  is 
broken.  It  makes  a  dynamo  fail  to  "  build  up  "  or  excite  its 
field,  or  give  the  proper  voltage  in  any  case.  A  motor  on  a 
constant-current  (arc)  circuit  would  probably  run  slowly  if 
the  field-magnetism  is  weak,  due  to  a  short-circuit  in  the 
field-coils,  or  some  other  cause. 

Symptom  and  Remedy  the  same  as  "Sparking,"  Cause 
8.  (See  the  following  Cause  ;  also  "  Dynamo  Fails  to  Gen- 
erate.") 

6.  Cause. —  Too  high  or  too  low  voltage  or  current  on  the 
circuit. 

Symptom. — This  would  cause  a  motor  to  run  too  fast  or 
'too  slow,  respectively.  It  can  be  proved  by  measuring  volt- 
age or  current  of  the  circuit. 

Remedy. — The  central  station  should  be  notified  that 
the  voltage  or  current  is  not  right. 

7.  Cause. — Motor  too  lightly  loaded. 

Symptom. — A  series-wound  motor  on  a  constant-potential 
circuit,  or  any  motor  on  a  constant-current  circuit,  is  liable 
to  run  too  fast  if  the  load  is  very  much  reduced,  or  removed 
entirely  (by  the  breaking  of  the  belt,  for  example). 

Remedy. — Care  should  be  exercised  in  using  a  series 
motor  on  a  constant-potential  circuit,  except  where  the  load 
is  a  fan,  pump,  or  other  machine  that  is  positively  connected 
or  geared  to  the  motor,  so  that  there  is  no  danger  of  its  being 
taken  off.  A  shunt  motor  should  be  used  if  the  load  is  likely 
to  be  thrown  off.  On  a  constant-current  circuit  a  motor 
must  be  provided  with  an  automatic  governor  or  cut-out, 
which  acts  to  reduce  the  power  if  the  speed  becomes  too 
great.  This  applies  to  all  constant-current  motors,  except 
those  to  which  the  load  is  positively  connected,  so  that  it  will 
never  be  thrown  off. 


152  Practical  Management  of 


CHAPTER  XXVII. 
MOTOR  STOPS  OR  FAILS  TO  START. 

THIS  is  an  extreme  case  of  the  previous  class  ("  Speed 
Too  High  or  Too  Low  "),  but  it  is  separated  because  it  is 
more  definite  and  permits  of  quicker  diagnosis  and  treat- 
ment. This  heading  does  not,  of  course,  apply  to  dynamos, 
since  any  trouble  in  setting  them  in  motion  is  outside  of 
the  machine  itself. 

1.  Cause. — Great  overload.     (See  "  Sparking/'  Cause  i.) 
—A  slight  overload  causes  motor  to  run  slowly,  but  an  ex- 
treme overload  will,  of  course,  stop  it  entirely  or  "  stall "  it. 

Symptom. — On  a  constant-current  circuit  no  harm 
results,  and  motor  starts  properly  when  load  is  reduced  or 
taken  off. 

On  a  constant-potential  circuit  the  current  is  excessive, 
and  safety-fuse  melts,  or,  in  the  absence  or  failure  of  the 
latter  to  act,  armature  is  burnt  out. 

Remedy. — Turn  off  switch  instantly,  reduce  or  take  off 
the  load,  replace  the  fuse  or  cut-out  if  necessary,  and  turn 
on  current  again  just  long  enough  to  see  if  trouble  still 
exists ;  if  so,  take  off  more  load. 

2.  Cause. —  Very  excessive  friction  due  to  shaft,  bearings, 
or  other  parts  being  jammed,  or  armature  touching  pole-pieces. 

Symptom. — Similar  to  previous  case,  but  is  distinguished 
from  it  by  the  fact  that  armature  is  hard  to  turn  by  hand, 
even  when  load  is  taken  off.  Examination  shows  that  the 
shaft  is  too  large,  bent,  or  rough,  or  that  the  bearing  is  too 
tight,- that  the  armature  touches  pole-pieces,  or  that  there  is 
some  other  impediment  to  free  rotation.  (See  "  Heating  of 
Bearings"  and  "Noise.") 


Dynamos  and  Motors.  153 

Remedy. — Turn  current  off  instantly,  asceitain  and  re- 
move the  cause  of  friction,  turn  on  the  current  again  just 
long  enough  to  see  if  trouble  still  exists  ;  if  so,  investigate 
further. 

3.  Cause. — Circuit  open,  due  to  (a)  safety-fuse  melted, 
(#)  wire  in  motor  broken  or  slipped  out  of  connections,  (c) 
brushes  not  in  contact  with  commutator,  (d)  switch  open,  (e) 
circuit  supplying  motor  open,  (/)  failure  at  generating 
station. 

Symptom. — Distinguished  from  Causes  I  and  2  by  the 
fact  that  if  the  load  is  taken  off  the  motor  still  refuses  to 
start,  and  yet  armature  turns  freely  by  hand. 

On  a  constant-current  circuit  the  switch  arcs  badly  when 
turned  on  if  motor  circuit  is  open  ;  but  there  is  no  current, 
motion,  or  other  effect  in  motor.  On  a  constant-potential 
circuit  the  field  circuit  alone  of  a  shunt  motor  may  be  open, 
in  which  case  the  pole-pieces  are  not  strongly  magnetic 
when  tested  with  a  piece  of  iron,  and  there  is  a  dangerously 
heavy  current  in  the  armature ;  if  the  armature  circuit  is  at 
fault  there  is  no  spark  when  the  brushes  are  lifted,  and  if 
both  are  without  current  there  is  no  spark  when  switch  is 
opened.  -  One  should  be  very  careful  if  there  is  no  field 
magnetism  or  even  if  it  is  weak,  as  a  motor  is  apt  to  be  burnt 
out  if  the  current  is  thrown  upon  its  armature  then. 

Remedy. — Turn  current  off  instantly.  Examine  safety- 
fuse,  wires,  brushes,  switch,  and  circuit  generally,  for  break 
or  fault.  If  none  can  be  found,  turn  on  switch  again  for  a 
moment,  as  the  trouble  may  have  been  due  to  a  temporary 
stoppage  of  the  current  at  the  station  or  on  the  line.  If 
motor  still  seems  dead,  test  separately  armature,  field-coils 
and  other  parts  of  circuit  for  continuity  with  a  magneto  or  a 
cell  of  battery  and  an  electric  bell  to  see  if  there  is  any  break 
in  the  circuit.  (See  "  Instructions  for  Testing,"  Part  II.) 

One  of  the  simplest  ways  to  find  whether  the  circuit  has 
current  on  it  and  to  locate  any  break,  is  to  test  with  an  incan 
descent  lamp.     Two  or  five  lamps  in  series  should  be  used 
on  220  and  500  volt  circuits,  respectively. 


154  Practical  Management  of 

4.  Cause. —  Wrong  connection  or  complete  short-circuit  of 
field,  armature,  switch,  etc. 

Symptom. — Distinguished  from  Causes  i  and  2  in  the 
same  way  as  Cause  3,  and  differs  from  Cause  3  in  the  evi- 
dence of  strong  current  in  motor. 

On  a  constant-potential  circuit,  if  current  is  very  great,  it 
indicates  a  short  circuit.  If  the  field  is  at  fault  it  will  not 
be  strongly  magnetic. 

The  possible  complications  of  wrong  connections  are  so 
great  that  no  exact  rules  can  be  given.  Carefully  examine 
and  make  sure  of  the  correctness  of  all  connections  (see  Dia- 
grams of  Connections).  This  trouble  is  usually  inexcusable, 
since  only  a  competent  person  should  ever  set  up  a  motor  or 
change  its  connections. 

In  the  three-wire  (22O-volt  direct-current)  system  several 
peculiar  conditions  may  exist,  as  follows : 

(a)  The  dynamo  or  dynamos  on  one  side  of  the  system 
(page  62)  may  become  reversed,  so  that  both  of  the  outside 
wires  are  positive  or  negative.  In  that  case  a  motor  fed  in  the 
usual  way  from  the  two  outside  conductors  will  get  no  cur- 
rent, but  lamps  connected  between  the  middle  or  "neutral" 
wire  and  either  of  the  outside  wires  will  burn  perfectly. 

(ft)  If  one  of  the  outside  wires  is  open  by  the  "  blowing" 
of  a  fuse,  an  accidental  break,  or  other  cause,  then  a  motor 
(220  volt)  beyond  the  break  can  get  some  current  at  no 
volts  through  any  lamps  that  may  be  on  the  same  side  of  the 
break  as  itself,  and  on  the  same  side  of  the  system  as  the 
conductor  that  is  open.  These  lamps  will  light  up  when  the 
motor  is  connected,  but  the  motor  will  have  little  or  no 
power  unless  the  number  of  lamps  is  very  great. 

(c)  If  the  neutral  or  middle  wire  is  open,  a  motor  con- 
nected with  the  outside  wires  will  run  as  usual;  but  lamps  on 
one  side  of  the  system  will  burn  more  brightly  than  those 
on  the  other  side,  unless  the  two  sides  are  perfectly  balanced. 

(d)  If  one  of  the   outside  wires  becomes  accidentally 
grounded,  a  no-volt  dynamo,  motor,  or  other  apparatus,  also 
grounded  and  connected  to  the  other  outside  wire,  will  re- 
ceive 220  volts,  which  will  be  likely  to  burn  it  out. 


Dynamos  and  Motors.  155 


CHAPTER  XXVIII. 

DYNAMO  FAILS  TO  GENERATE. 

THIS  trouble  is  almost  always  caused  by  the  inability  of 
a  dynamo  to  sufficiently  "  excite"  or  "build  up  "  its  field- 
magnetism.  The  proper  starting  of  a  self-exciting  dynamo 
requires  a  certain  amount  of  residual  magnetism,  which 
must  be  increased  to  full  strength  by  the  current  generated 
in  the  machine  itself.  This  trouble  is  not  likely  to  occur  in 
a  separately  excited  machine,  and  if  it  does  it  is  usually  due 
to  the  exciter  failing  to  generate,  and  therefore  amounts  to 
the  same  thing. 

I.  Cause. — Residual  magnetism  too  ^veak  or  destroyed, 
due  to  (a)  vibration  or  jar,  (b)  proximity  of  another  dynamo, 
(c)  earth's  magnetism,  (d)  accidental  reversed  current  through 
fields,  not  enough  to  completely  reverse  magnetism.  The 
complete  reversal  of  the  residual  magnetism  in  any  dynamo 
will  not  prevent  its  generating,  but  will  only  make  it  build  up 
a  current  of  opposite  polarity.  Sometimes  reversal  of  residual 
magnetism  may  be  very  objectionable,  as  in  case  of  charging 
storage-batteries;  but,  although  the  popular  supposition  is 
to  the  contrary,  it  will  not  cause  the  machine  to  fail  to 
generate. 

Symptom. — Little  or  no  magnetic  attraction  when  the 
pole-pieces  are  tested  with  a  piece  of  iron. 

Remedy. — Send  a  magnetizing  current  from  another  ma- 
chine or  battery  through  field-coils,  then  start  and  try  ma- 
chine ;  if  this  fails,  apply  the  current  in  the  opposite  direc- 
tion since  the  magnets  may  have  enough  polarity  to  prevent 
the  battery  building  them  up  in  the  direction  first  tried. 

Shift  the  brushes  backward  from  the  neutral  point  to 


156  Practical  Management  of 

make  armature  magnetism  assist  field.  Turn  machine  around 
or  change  its  polarity,  so  that  the  magnetism  which  the  earth 
or  the  adjacent  machine  tends  to  induce  is  in  harmony. 
Dynamos  should  be  placed  with  their  opposite  poles  toward 
each  other,  and  the  north  pole  of  a  machine  should  prefer- 
ably be  placed  toward  the  North  (which  is  magnetically  the 
south  pole  of  the  earth),  but  the  earth's  magnetism  is  hardly 
strong  enough  to  reverse  a  dynamo's  residual  magnetism. 

2.  Cause. — Reversed  connections  or  reversed  direction  of 
rotation. 

Symptom. — When  running,  pole-pieces  show  no  attrac- 
tion for  a  piece  of  iron.  The  application  of  external  current 
cannot  be  made  to  start  the  machine,  as  in  Cause  r,  because 
whichever  way  field  might  be  thus  magnetized  the  resulting 
current  then  generated  by  armature  opposes  and  destroys 
the  magnetism. 

Remedy. — (a)  Reverse  either  armature  connections  or 
field  connections,  but  not  both.  (&)  Move  brushes  through 
1 80°  for  two-pole,  90°  for  four-pole  machines,  etc.  (See  page 
44.)  (c)  Reverse  direction  of  rotation.  After  each  of  the 
above  the  field  may  have  to  be  build  up  with  a  battery  or 
other  current,  since  the  causes  of  this  case  operate  to  destroy 
whatever  residual  magnetism  may  have  been  present. 

3.  Cause. — Short-circuit  in  the  machine  or  external  cir- 
cuit. 

Symptom. — Magnetism  weak,  but  usually  perceptible. 

Remedy. — If  short-circuit  is  in  the  external  circuit,  it 
will  prevent  the  building  up  of  a  shunt  dynamo  until  switch 
on  external  circuit  is  opened.  But  with  a  series  dynamo  it 
will  hasten  the  "building  up."  If  the  short-circuit  is  within 
the  machine,  it  is  likely  to  prevent  the  building  up  of  either 
shunt  or  series  machines,  and  it  should  be  found  by  careful 
inspection  or  testing.  In  these  cases  do  not  connect  the 
external  circuit  till  short-circuit  is  found  and  eliminated.  A 
slight  short-circuit,  such  as  that  caused  by  a  defective  lamp 
socket  or  copper  dust  on  the  brush-holder  or  commutator, 
may  prevent  a  shunt  machine's  magnetism  from  building  up. 


Dynamos  and  Motors.  157 

r 

(See  "  Sparking,"  Causes  5  and  8.)  Too  many  lamps  or 
other  load  might  prevent  a  shunt  dynarro  from  building  up 
its  field-magnetism,  in  which  case  the  lead  should  be  dis- 
connected in  starting. 

4.  Cause.  —  Field-coils  opposed  to  each  other. 

Symptom.  —  Upon  passing  a  current  from  another  dyna- 
mo or  a  battery  the  following  symptom  will  exist  :  If  the 
pole-pieces  of  a  bipolar  machine  are  approached  with  a 
compass  or  other  freely  suspended  magnet,  they  both  attract 
the  same  end  of  the  magnet,  showing  them  both  to  be  of 
the  same,  whereas  they  should  always  be  of  opposite, 
polarity. 

For  similar  reasons  the  pole-pieces  are  magnetic  when 
tested  separately  with  a  piece  of  iron,  but  show  less  attrac- 
tion when  the  same  piece  of  iron  is  applied  to  both  pole- 
pieces  at  once,  in  which  latter  case  the  attraction  should  be 
stronger.  In  m  u  It  i  polar  machines  these  tests  should  be 
applied  to  consecutive  pole-pieces. 

Remedy.  —  Reverse  the  connections  of  one  of  the  coils  in 
order  to  make  the  polarity  of  the  pole-pieces  opposite.  The 
pole-pieces  should  be  alternately  north  and  south  (when 
tested  by  compass)  in  practically  all  dynamos  and  motors. 

5.  Cause.  —  Open  circuit. 

(a)  Broken  wire  or  faulty  connection  in  machine,  (b) 
brushes  not  in  contact  with  commutator,  (c)  safety-fuse 
melted  or  absent,  (d)  switch  open,  (e)  external  circuit  open. 

Symptom.  —  If  the  trouble  is  merely  due  to  the  switch  or 
external  circuit  being  open,  the  magnetism  of  a  shunt  dyna- 
mo may  be  at  full  strength,  and  the  machine  itself  may  be 
working  perfectly  ;  but  if  the  trouble  is  in  the  machine,  the 
field-magnetism  will  probably  be  very  weak. 

Remedy.  —  Make  very  careful  examination  for  open 
circuit  ;  if  not  found,  test  separately  the  field-coils,  arma- 
ture, etc.,  for  continuity  with  magneto  or  cell  of  battery  and 
electric  bell.  (See  "  Instructions  for  Testing,"  Part  II,  and 
also  "  Motor  Stops,"  etc.,  Cause  3.) 


UNIVERSITY 


158  Practical  Management  of 

» 

A  break,  poor  contact,  or  excessive  resistance  in  the  field 
circuit  or  regulator  of  a  shunt  dynamo  will  also  make  the 
magnetism  weak  and  prevent  its  building  up.  This  may  be 
detected  and  overcome  by  cutting  out  the  rheostat  for  a 
moment  by  connecting  the  two  terminals  of  the  field-coils 
to  the  two  brushes,  respectively,  care  being  taken  not  to 
make  a  short-circuit. 

A  break  or  abnormally  high  resistance  anywhere  in  the 
circuit  of  a  series-wound  dynamo  will  prevent  it  from  gen- 
erating, since  the  field-coil  is  in  the  main  circuit.  This  may 
be  detected  and  overcome  by  short-circuiting  the  machine 
for  a  moment  in  order  to  start  up  the  magnetism. 

Either  of  these  two  remedies  by  short-circuiting  should 
be  applied  very  carefully,  and  not  until  the  pole-pieces  have 
been  tested  with  a  piece  of  iron  to  make  sure  that  the  mag- 
netism is  weak. 

6.  Cause. — Brushes  not  in  proper  position. 

Symptom. — The  magnetism  and  current  are  increased 
by  shifting  the  brushes. 

Remedy. — It  often  happens  that  the  brushes  are  not  set 
at  the  proper  point ;  in  fact,  they  may  be  set  exactly  wrong, 
so  that  the  dynamo  is  incapable  of  generating  any  current 
whatever.  This  trouble  is  mainly  due  to  the  fact  that  the 
proper  position  for  the  brushes  is  not  the  same  for  all  kinds 
of  machines.  Almost  all  ring  armatures  and  many  drum 
armatures  require  the  brushes  to  be  set  opposite  the  spaces 
between  the  pole-pieces.  But  Edison,  Sprague,  and  some 
other  drum  armatures  are  wound  so  that  the  brushes  have 
to  be  set  nearly  at  right  angles  to  this  position,  and  T.  H. 
machines  at  about  45°.  Some  multipolar  machines  have  as 
many  sets  of  brushes  as  there  are  pole-pieces,  while  others 
have  armatures  which  are  cross-connected,  or  have  the  con- 
ductors arranged  in  series  so  that  only  two  sets  of  brushes 
are  required.  Four-pole  machines  with  only  two  brushes 
require  them  to  be  set  at  90° ;  six-pole  machines,  either  60° 
or  180°;  eight-pole,  either  45°  or  135°;  ten-pole,  either  36°, 
108°,  or  180°;  twelve-pole,  either  30°,  90°,  or  130°;  and 
sixteen-pole,  either  22^°,  6;i°,  112^°,  or  157^°;  and  so  on. 


Dynamos  and  Motors.  159 

In  machines  having  two  brushes  they  may  be  set  directly 
opposite  (i.e.,  180°)  whenever  the  number  of  poles  is  twice 
an  odd  number. 

The  fact  is,  that  the  proper  position  of  the  brushes  de- 
pends upon  the  particular  winding,  internal  connections,  etc., 
and  no  one  should  ever  assume  to  know  where  to  set  the  brushes 
unless  he  is  perfectly  familiar  with  the  particular  type  of 
machine.  A  blue  print  or  other  definite  instructions  should 
always  be  obtained  and  followed,  and  if  these  are  not  avail- 
able the  matter  may  be  determined  by  careful  trial.  The 
proper  position  of  brushes  is  the  same  for  dynamos  and 
motors,  except  that  in  the  former  the  brushes  are  given  a 
"  forward  lead,"  that  is,  shifted  a  little  in  the  direction  of 
rotation,  whereas  motor  brushes  should  be  set  a  little  back- 
ward. This  shifting  is  necessitated  by  the  armature  reac- 
tion or  the  magnetizing  effect  of  the  armature  current,  which 
to  a  certain  extent  distorts  the  field-magnetism. 

The  positions  and  number  of  brushes  for  each  kind  of  ar- 
mature is  shown  in  Fig.  72,  which  shows  also  the  arrange- 
ments of  circuits  in  each  of  the  leading  types. 

A  is  the  armature  for  the  ordinary  two-pole  machine,  and 
may  be  drum  or  ring  wound.  The  current  enters  from  the 
positive  brush,  passes  around  both  sides  of  the  armature,  and 
out  through  the  negative  brush.  Hence  this  is  called  a  two- 
circuit  armature. 

B  is  a  plain  armature  used  in  a  four-pole  machine.  As 
there  are  two  more  poles,  it  is  necessary  to  use  two  more 
brushes  to  collect  the  currents.  This  gives  two  brushes 
through  which  current  enters  and  two  through  which  it 
leaves  ;  consequently  each  pair  of  brushes  must  be  joined 
in  multiple  in  order  to  carry  all  the  current  to  the 
mains. 

C  is  a  four-pole  armature  in  which  the  additional  cur- 
rents are  carried  across  to  the  first  pair  of  brushes  by  means 
of  connections  through  the  centre  of  the  armature.  There- 
fore the  entire  current  may  be  taken  off  by  these  brushes, 
or  two  more  may  be  added  to  divide  the  work,  in  which  case 
they  must  also  be  connected  in  multiple  to  the  first  pair,  as 
in  case  B. 

With  either  B  or  (7,  since  there  are  two  parts  of  the 


i6o 


Practical  Management  of 


Two  Pole,  TWO  Circuit 


four  Pole,  Four  Circuit,  Four  Brushes., 
In  Multiple; 


Four  Pole,  Four  Circuit  Cross  Connected 

Two  Brushes  or  Four  Brushes, 

In  Multiple. 


Four  Pole.'Two  Circuit  Ring 
Two  Brushes  or  Four 
In  Multiple. 


F    Pit 


Four  Pole,  Two  Circuit  Drum 

Two  Brushes  or  Four  Brushes, 

In  Multiple. 


Eight  Pole,  Two  Circuit  Drum 

Two  Brushes,  or  Four, 

Six  or  Eight  Brushes, 

In  Multiple. 


FIG.  72. — PRINCIPLES  OF  THE  CONNECTIONS  IN  THE  DIFFERENT  TYPES 
OF  ARMATURES. 


Dynamos 

armature  winding,  under  the  influence  of  different  magnets, 
•  but  running  in  parallel  to  the  mains,  it  is  evident  that  if 
the  pressure  of  the  current  in  one  part  of  the  winding  is 
weaker  than  in  the  other,  through  inequality  of  the  magnets 
or  otherwise,  it  will  short-circuit  the  other  part  of  the  wind- 
ing and  work  badly. 

This  cannot  occur  in  A,  because  both  parts  of  the  wind- 
ing are  influenced  by  the  two  ends  of  a  single  magnet. 

D  is  a  four-pole  armature  in  which  the  windings  do  not 
connect  together  in  parallel  but  in  series,  thus  overcoming 
the  objection  above.  It  is  a  ring-winding,  and  each  coil  is 
connected  to  the  one  diametrically  opposite,  giving  the 
effect  of  a  single  coil  of  twice  the  size  under  a  single  mag- 
net of  double  size,  instead  of  two  smaller  ones  of  one 
polarity. 

An  examination  will  show  that  though  the  poles  alter- 
nate, the  wire  is  all  arranged  so  that  the  current  flows  in  a 
single  pair  of  circuits,  as  in  A.  This  also  permits  of  the  use 
of  larger  wire  and  fewer  turns,  as  they  are  connected  in 
series  instead  of  multiple. 


FIG.  720. — 40  H.P.  CROCKER-WHEELER  FOUR-POLE  BAR  WOUND  DRUM 
ARMATURE,  using  no  wire  or  solder.  Bars  sunk  in  slots  in  iron  core 
(Type  E,  Fig.  72). 

E  is  a  drum  armature  all  in  series,  as  with  D.  This 
winding  is  made  with  bars  instead  of  wire.  Inspection  will 
show  that  the  action  of  each  of  the  four  poles  on  all  the 
bars  harmonize,  or  cause  the  current  to  flow  in  the  same 
direction. 

The  bars  pass  through  slot*  in  the  periphery  of  the  arma- 
ture, and  their  ends  on  the  nearer  side  are  connected  to- 


1 6  2  Practical  Management  of 

gether  by  the  solid  lines  and  the  ends  on  the  other  side  of 
the  armature  by  the  dotted  lines.  (Fig.  72^.) 

To  facilitate  tracing  the  course  of  the  current,  the  ar- 
rangement is  represented  with  the  smallest  possible  number 
of  bars.  About  ten  times  as  many  are  used  in  practice. 

.Fis  a  series  bar-wound  drum  armature  for  eight  poles. 
The  principle  is  the  same,  but  the  limit  of  brush  adjustment 
is  smaller.  The  entire  range  from  o  to  full  E.  M.  F.  is 
covered  by  moving  the  brush  \  of  the  circumference. 

As  the  winding  is  all  in  series,  two  brushes  only  are  neces- 
sary, but  as  many  more  as  desired  may  be  added  between 
the  other  poles,  and  then  connected  in  multiple  to  the  first 
ones.  This  is  usually  taken  advantage  of,  because  the  single 
pair  of  brushes  would  become  heated  from  carrying  exces- 
sive current,  but  the  difficulty  of  one  part  of  the  armature 
short-circuiting  the  other  cannot  occur,  because  each  part 
of  the  winding  is  under  the  influence  of  all  the  poles. 

CONCLUSION. 

In  the  treatment  of  diseases  of  motors  and  dynamos  it  is 
evidently  impossible  to  give  complete  directions  for  every 
case.  But  it  will  be  found  that  nearly  all  causes  of  trouble 
have  been  covered,  the  exceptions  being  for  the  most  part 
in  certain  special  forms  of  machines.  A  mere  list  of  these 
troubles,  particularly  if  it  is  systematically  arranged,  is  of  the 
greatest  help,  and  promptness  and  intelligence  in  dealing 
with  troubles  or  accidents  are  the  best  proofs  of  an  en- 
gineer's knowledge  and  ability. 


Dynamos  and  Motors.  163 


PART  IV. 
Arc  Dynamos   and  Holers   Requiring  Especial    Directions. 

Giving  only  those  features  which  are  special  for  each  machine,  general 
features  being  covered  in  main  part  of  book. 

CHAPTER  XXIX. 

THE  THOMSON-HOUSTON  ARC  DYNAMO. 
By  HORATIO  A.  FOSTER. 

PREFACE. — The  length  of  the  following  chapters  need  not 
alarm  the  dynamo  man,  but  rather  win  his  confidence,  as  it  is 
the  result  of  a  desire  for  completeness.  No  one  dynamo 
ever  has  all  the  diseases  described  ;  in  fact  they  rarely  have 
more  than  one  or  two  at  a  time  and  many  of  the  symptoms 
merely  cause  annoyance  to  the  careful  dynamo  man.  The 
attempt  has  been  made  to  cover  the  field  thoroughly,  but 
the  individual  machine  should  be  studied  carefully  before 
attempting  to  apply  the  remedies.  The  directions  peculiar 
for  left-hand  dynamos  are  given  separately  on  page  1 79  to 
avoid  confusion.  They  are  similar  but  reversed,  and  special 
fittings  are  required.  It  is  much  easier  to  turn  the  regular 
machine  end  for  end  before  belting  up,  if  necessary,  to  make 
its  direction  of  rotation  agree  with  the  driving  pulley,  than 
to  reverse  its  rotation. 

DIRECTIONS   FOR  SETTING  UP.     , 
See  the  general  directions  given  in  Part  I. 
The  speed  should  be  that  recommended  by  the  manu- 
facturer, but  a  slight  departure  from  this  does  no  harm,  un- 
less high   enough  to  endanger  bursting  or  low  enough  to 
cause  flashing.     Increased  speed  increases  ventilation. 


164 


Practical  Management  of 


ADJUSTMENTS. 

The  Air-blast  or  Blower,  (Fig.  80)  is  attached  to  the 
back-plate  on  the  front  bearing  by  four  bolts,  a  (Fig.  82). 
The  armature  shaft  passes  through  the  hole  in  the  centre 
without  contact,  excepting  by  a  key  set  in  the  shaft  fitting 


FIG.  73.— T.  H.  ARC  DYNAMO. 

into  a  slot  in  the  blower  spider.    The  bearings  of  the  spider 
are  in  the  air-blast  casing. 

The  armature  shaft  is  sometimes  bent  out  of  line  at  the 
small  end :  this  can  be  detected  by  a  piece  of  thick  paper 
wound  around  the  shaft  and  inserted  under  the  blower 
bearing ;  the  space  should  be  clear  and  even  all  the  way 


Dynamos  and  Motors. 


165 


1 66  Practical  Management  of 

around  ;  if  not  so,  the  shaft  must  be  bent  back  to  place,  or 
the  back-plate  readjusted. 

Yokes  and  Sliding  Connections. — To  adjust :  Remove 
the  small  plate  from  front  bearing  of  air-blast,  clean  the 
yokes  and  attachments,  and  place  in  position  on  the  bear- 
ing ;  see  that  the  thin  iron  washer  is  between  the  two  brass 
yokes,  and  that  the  brush-holder  studs  are  outward,  away 
from  the  machine  ;  screw  the  plate  back  in  place,  and  see 
that  all  parts  work  freely  around  the  bearing.  Place  the 
two  longer  brush-holder  studs  in  the  back  yoke  ;  then  the 
clamps  will  all  be  in  line  around  the  commutator.  Secure 
the  sliding  connections  in  place  between  the  two  pairs  of 
brush-holder  studs ;  the  barrel  part  is  always  fastened  to 
the  top  stud.  The  screws  are  made  with  shoulders  so  that 
the  small  spring  with  each  end  of  the  connection  may  have 
room  for  action  and  the  connection  itself  be  perfectly  free 
in  all  positions  of  the  brushes. 

The  two  lower  brush-holder  studs  are  secured  to  the 
yokes  by  long  studs  in  place  of  nuts  ;  to  these  studs,  one  of 
which  is  longer  than  the  other  and  goes  on  the  outer  yoke, 
are  fastened  the  ends  of  the  rods  that  connect  the  field-ter- 
minals A  with  the  brushes,  as  shown  in  Fig.  73.  The 
other  ends  of  these  rods  are  to  be  fastened  to  the  field-ter- 
minal posts  A,  A\  and  care  must  be  taken  that  in  making 
this  joint  the  spring  is  first  placed  in  the  end  of  the  stud, 
the  small  brass  washer  coming  next  for  a  bearing  for  the 
rod,  and  the  large  flat-headed  screw  being  passed  through 
the  slot  in  the  rod  and  through  the  washer  and  spring,  and 
screwed  home. 

The  rod  should  have  a  flrm  bearing,  being  held  in  con- 
tact by  the  springs  at  either  end,  but  should  slide  freely 
endwise. 

The  field  terminals  and  binding-posts  A,  A\  P,  P*,  and 
N  are  easily  adjusted.  P2  is  secured  in  place  on  the  fibre 
bearings  provided,  and  will  only  fit  on  one  way.  For  each 
of  the  others  the  hard-wood  bushing  is  placed  in  the  hole 
in  the  casting ;  a  hard-rubber  washer,  with  recess  on  one 
side  fitting  over  the  shoulder  of  the  bushing,  is  placed  on 
either  side,  and  the  stud  of  the  binding-post  is  passed 
through  and  secured  in  place  by  a  nut. 


Dynamos  and  Motors.  \  6  7 

The  regulator  M  is  bolted  to  the  top  of  the  left  leg  as 
shown  in  Fig.  73  ;  the  arm  L  is  screwed  on  to  the  armature, 
and  the  curved  link  connecting  this  arm  to  the  yoke 
mechanism  is  allowed  to  swing  free.  The  bolt  on  the  top 
of  the  regulator  is  loosened  and  regulator  turned  until 
the  link  hangs  in  line  with  the  slide  connection  on  yoke, 
keeping  pole  of  magnet  well  centered  in  hole  in  armature  so 
as  not  to  touch;  the  top  bolt  is  then  tightened  and  the 
screw  fastening  link  to  yoke  is  inserted. 

Place  dash-pot  D  temporarily  in  position  and  work  whole 
regulator  mechanism  up  and  down  to  test  for  stickiness  or 
tight  fitting  before  putting  glycerine  in.  When  regulating 
system  works  freely,  remove  dash-pot  plunger  and  fill  about 
three-quarters  full  with  concentrated  glycerine ;  don't  use 
cylinder  oil  unless  you  have  had  much  experience ;  replace 
plunger  and  cap,  and  secure  the  whole  permanently  in  position. 

Terminal  Wires. — The  wire  of  the  left-hand  field-mag- 
net starts  from  the  terminal  post  P*,  reaching  the.  bottom 
layer  through  a  recess  in  the  casting,  the  lead  wire  of  the 
outer  layer  terminating  at  the  back  end  of  A  ;  the  right-hand 
field-wire  starts  at  N  and  terminates  at  A1,  being  fastened, 
like  the  outside  terminal  wire  of  left  field,  to  inner  end  of 
post  by  a  small  screw. 

The  short  terminal  wire  from  the  regulator  magnet  is  also 
secured  to,the  post  P*,  the  long  terminal  wire  of  the  same 
being  run  down  inside  the  frame  to  inner  end  of  post  P. 

Commutator. — The  lead  wires  emerging  from  end  of 
shaft  are  colored  red,  white,  and  blue  to  indicate  coils,  one, 
two,  and  three,  respectively ;  straighten'  them  out,  thor- 
oughly clean  the  commutator,  and  slip  it  onto  the  shaft  with 
the  terminal  posts  on  the  outside  ;  place  it  so  the  segments 
are  in  line  with  the  brush-holders,  and  turn  it  until  the 
chisel-mark  on  the  front  collar  exactly  coincides  with  the 
mark  on  the  shaft ;  then  tighten  the  six  set-screws.  Place 
the  red,  white,  and  blue  lead  wires  in  the  terminal  posts 
numbered  one,  two,  and  three,  respectively. 

To  adjust  a  new  commutator,  or  one  with  no  marks :  Af- 
ter placing  it  on  the  shaft,  adjust  the  brush-holder  studs  and 
the  top  negative  brush,  as  per  directions  following  this  ;  then 
proceed  as  follows:  First  find  the  thick  insulated  wire  which 


i68 


Practical  Management  of 


lies  in  the  division  between  the  two  sides  of,  and  is  the  lead 
wire  for,  the  number  one  or  outside  armature  coil  ;  ro- 
tate the  armature  to  the  left  until  this  wire  is  underneath  to 
the  right,  as  shown  in  Fig.  75,  and  the  right-hand  side  of 


PEG.  TO  ADJUST  COMMUTATOR  BY 


OLD   STYLE   ARMATURE 
LEAD    FOR 

V.  M    L.  ^  IN.  NEGATIVE 
M.  D.       T76    "     POS.'TIVE 
L.  D.         %    " 
K.  H    E.    V±    " 


(See  Fig-.  76 
for  leads  for 
ring  arma- 
tures.) 


THIS   DISTANCE,   NAMELY 

BETWEEN   POINT  OF  SEGMENT 

NO.  2   AND  POINT  OF  BRUSH 

S  CALLED  THE  LEAD 


FIG.  75. 

peg  on  the  right  of  coil  number  one  is  just  in  line  with  edge 
of  left  field,  as  shown  in  the  same  figure ;  then  turn  commu- 
tator until  the  segment  numbered  one  is  in  a  position  oppo- 
site to  coil  number  one  and  the  slot  edge  of  number  two 
segment  projects  beyond  and  to  the  left  of  the  tip  of  the 
top  negative  brush  the  distance  or  lead  as  given  in  Fig.  75  ; 
tighten  the  set-screws  in  each  end  of  commutator,  secure 
lead  wires  in  proper -holes,  and  test  for  correct  spark  by  run- 
ning up  to  speed  with  full  load. 

In  the  new-style  ring  armatures  the  peg  is  replaced  by  a 


Dynamos  and  Motors. 


169 


black  mark  painted  on  the  armature  or  by  a  double-pointed 
tin   arrow  secured  to  the  centre  band,  the  points  of  which 
are  to  be  brought  into  line  with  the  edge  of  field  in  the  same 
manner  as  the  side  of  the  peg  is  used  (Fig.  76). 
Black  mark  to  use  in  place  of 


Leads  for  ring-pattern  armature. 
M.D.        ~  y\  positive. 
L.D.I2     =   £ 
L.D.2       =   i 
M.I 2        =   %  negative. 
M.2         =  i        " 

FIG.  76, — CONNECTIONS,  COMMUTATOR  END,  RING-PATTERN  ARC  ARMATURE. 

It  must  be  understood  that  this  adjustment  of  the  com- 
mutator is  only  preliminary  and  approximate,  and  that  the 
real  and  accurate  adjustment  is  done  by  test  under  full  load 
in  order  to  regulate  the  proper  length  of  spark ;  as  the  iron 
varies  in  different  machines,  the  length  of  lead  to  give  the 
best  results  will  also  vary.  In  the  new  ring  armatures  the 
lead  in  many  cases  is  negative,  that  is,  the  edge  of  segment 
is  to  the  right  of  and  under  the  top  brush. 

Full  load  is  indicated  when  the  bottom  of  regulator  ar- 
mature remains  at  £  inch  above  the  stop,  which  is  a  small 
projection  on  the  brass  cross-bar  underneath  it. 


170 


Practical  Management  of 


The  normal  spark  at  full  load  is  about  T\  inch  long  from 
the  tips  of  top  and  bottom  brushes,  no  spark  showing  on  the 
side  brushes:  if  less  than  this  length,  the  machine  is  apt  to 
flash,  and  the  commutator  must  be  turned  a  trifle  in  the 
direction  of  rotation;  if  longer  than  T3^-  inch,  the  capacity  in 
voltage  is  lessened,  as  also  is  flashing,  and  commutator  should 
be  shifted  backward. 

Brush-holder. — Adjustment :  A  brush-holder  gauge  (Fig. 
77)  is  provided  with  each  dynamo. 

The  curved  surfaces  are  turned  to  same  radius  as  the 
commutator.  The  gauge  being  placed  on  the  surface  of 

commutator,  the  flat  bearing- 
surface  of  each  brush -holder 
must  be  brought  to  coincide  ex- 
actly with  the  straight  edge  of 
the  gauge,  and  securely  fastened 
by  tightening  the  nuts  and  studs 
back  of  the  yokes  ;  the  lips  of 
all  the  holders  must  be  care- 
fully tested  for  distance  from 
the  commutator,  by  marking  with  the  sharp  point  of  a  knife- 
blade  a  point  z  on  the  straight  edge.  This  distance  must  be 
the  same  for  all  yokes.  If  it  does  not  show  so  on  gauge, 
either  yokes  are  bent  or  wood  bushings  are  not  central  with 
holes  in  yokes.  This  should  be  investigated  and  remedied. 
Brush  Gauge  consists  of  a  strip  of  sheet  brass  about  an 


FIG.  77. — BRUSH-HOLDER  GAUGE. 


inch  wide  and  of  the  proper  length  for 
the  brush  to  project  beyond  the  lip  of 
the  holder,  as  shown  at  /,  Fig.  78.  All 


FIG   78. 


Dynamos  and  Motors.  171 

brushes  must  be  perfectly  straight  before  setting,  and  must 
be  set  by  this  gauge. 

The  lengths  of  gauges  for  the  different  sizes  of  machines 
are  as  follows : 

C.  =  3T33-  inches  ;  E.2  =  ^\\  inches. 

E.I 2,  H.,  L.,  M.,  L.D.,  M.  D.,  each  =  4^  inches. 

P.  =  4j^-  inches. 

Cut-out. — Adjustment :  The  relation  of  brushes  and  com- 
mutator segments  is  such  that  with  the  proper  adjustment 
two  armature  coils  are  in  multiple,  and  this  pair  is  in  series 
with  the  third  coil. 

The  relation  is  also  such  that,  excepting  when  the  regu- 
lator is  down  on  the  stop,  the  armature  is  short-circuited  six 
times  in  each  revolution,  by  each  segment  reaching  from 
brush  Bl  to  brush  B\  and  from  B*  to  B*  (Fig.  79),  the  dura- 


FIG.  79.— ADJUSTMENT  OF  CUT-OUT. 

tion  of  this  short-circuit  being  determined  by  the  position  of 
the  regulator. 

Adjust  as  follows  :  Lower  regulator  to  the  stop  ;  in  this 
position,  with  straight  brushes  carefully  set  by  gauge  and 
with  brush-holders  set  at  the  proper  angle  and  distance,  the 
commutator  must  be  turned  in  the  direction  of  rotation  un- 
til point  £*just  comes  in  contact  with  the  brush  B" ;  the  tip 
of  brush  Bl  should  then  project  over  the  edge  of  the  follow- 
ing segment  ^  inch. 


172 


Practical  Management  of 


Take  care  that  the  contact  at  C  is  just  a  contact,  and  no 
more.  This  is  best  determined  by  placing  a  light  or  a  piece 
of  white  paper  back  of  the  commutator  while  adjusting. 

All  segments  must  be  tried  in  this  manner  on  brush  J3\  ; 
Ihen  the  test  must  be  repeated,  using  brush  B*  in  place  of  B\ 
the  cut-out  now  being  shown  at  the  tip  of  brush  />".  Should 
the  tip  D  of  brush  Bl  or  B*  project  further  across  the  slot 
than  -gl¥  inch,  the  cut-out  is  called  weak,  and  the  adjusting 
slide  on  the  yoke  connecting  with  the  regulator-arm  must 
be  loosened  and  raised  slightly.  If  the  tips  of  the  above- 
mentioned  brushes  are  back  further,  and  do  not  project  into 
the  slot  at  all,  the  cut-out  is  strong,  and  the  slide  is  lowered 
to  correct  it. 

Weak  cut-out  decreases  the  voltage  capacity;  strong 
cut-out  endangers  'flashing.  Each  machine  needs  its  own 
special  adjustment  for  best  working. 

Air-blast,  Wings,  and  Jets. — Adjustment :  The  air-blast 


FIG.  80.— THE  AIR-BLAST. 


or  blower  as  seen  in  Fig.  80  is  a  rotary  blower,  having  hard- 
rubber  wings  fitted  loosely  into  the  slots  in  the  hub,  filling 
them  flush  with  the  periphery  of  the  hub:  as  the  hub  is 
turned  the  wings  are  thrown  outwardly  by  centrifugal  force 
against  the  inner  surface  of  the  chamber,  forcing  the  air  which 


Dynamos  and  Motors. 


173 


has  entered  through  the  screen-protected  holes,  B,  Fig.  81, 
into  the  outlets  leading  to  the  jets.  Jets  must  be  set  at  the 
right  point,  and  blower  must  be  so  adjusted  as  to  deliver 
the  strongest  blast  at  the  moment  of  sparking,  and  the 


D. 


FIG.  81.— (A)  AIR-BLAST  WING  FOR  SMALL  BLOWERS.  (See  FIG.  82.)  (B)  IN- 
LET SCREEN,  (c)  AIR-BLAST  JET.  (D)  AIR-BLAST  WING  FOR  LARGE  BLOW- 
ERS. (See  FIG.  84.) 

bolt-holes  are  located  to  do  this ;  the  slots  in  the  back-plate 
for  the  bolts  a,  Fig.  82,  allow  any  slight  adjustment  needed. 
The  outer  or  rubbing  edge  of  the  wings  A  or  D,  Fig.  81,  is 
rounded  off  in  a  peculiar  form,  the  forward  side  being  high- 
est ;  this  high  side  must  always  be  placed  forward  in  direction 
of  rotation. 

Carefully  clean  the  jets  C,  see  that  the  delivery  slots  are 
clear,  place  them  in  the  holes  provided  ;  loosen  the  four 
bolts  A  on  the  back-plate.  The  brushes 
being  set  by  gauge,  lift  the  regulator-arm 
to  highest  point,  then  turn  blower  and 
jets  so  the  tip  D  of  the  jet  is  on  a  per- 
pendicular line  with  the  tip  P  of  top 
brush  (see  Figs.  82  and  84,  which  show 
exact  position  of  jets),  and  the  tip  of  the 
jet  clears  the  segments  -fa  inch.  Tighten 
bolts  a,  fasten  jets  in  position  with  the  thumb-screws,  and 
set  the  lower  jet  in  same  relative  position  with  lower  brush. 

As  segments  wear  down,  air-blast  must  be  turned  to  the 
right,  as  shown  in  Figs.  83  and  85,  to  follow  up  the  change 
in  position  of  brushes. 

Wall  Controller. — This  must  be  fastened  to  a  firm  per- 
pendicular support  and  stand  plumb,  so  that  the  cores  of  the 
solenoids  hang  central  and  work  freely. 


or 
JET    DELIVERY. 


174 


Practical  Management  of 


WITH  HEW  SEGMENTS. 


FlG.   82. 


WlTH   SEGMENTS   MUCH   WORN. 


Dynamos  and  Motors. 


OF   THE 

UNIVERSITY 


FIG.  84. 


FIG.  85. 


1 76  Practical  Management  of 

Connect  binding-posts  P  and  P*  (Fig.  86)  to  binding- 
posts  on  the  dynamo  lettered  the  same.  A  convenient  way 
to  remember  is,  that  when  the  box  faces  the  commutator 
side  of  the  dynamo  the  wires  run  straight. 

Do  not  remove  packing-blocks  and  wedges  until  the  box 
is  permanently  secured  in  position. 

See  that  the  carbon  resistance  in  right  side  of  box  is 
intact  ;  this  is  a  shunt  around  contacts  O,  and  if  broken  bad 
sparking  takes  place  between  them. 

See  that  no  screws  are  strained  or  loosened  ;  that  the  con- 
tacts O  are  separated  -^  inch  when  cores  are  lifted  to  top  ;  if 
not,  bend  lower  contact  down. 

The  operation  of  the  controller  is  as  follows:  When  the 
contacts  O  are  closed  the  regulator  magnet  M,  Fig.  73,  is 
short-circuited,  its  armature  falls,  and  more  pressure  is  gene- 
rated in  the  dynamo  ;  as  the  full  current  from  the  machine 
goes  through  magnets  C  of  the  controller,  when  it  exceeds 
the  normal  amount  for  which  the  instrument  is  adjusted  by 
spring  5,  these  magnets  lift  the  cores,  break  the  contact  at 
O,  and  current  again  flows  around  the  regulator  magnet,  lift- 
ing its  armature,  shifting  the  brushes  into  position  to  gener- 
ate less  pressure,  until  less  than  the  normal  current  flows, 
when  the  cores  C  fall,  closing  contact  O,  again  short-circuit- 
ing the  regulator,  and  the  entire  operation  is  repeated.  The 
regulating  system  is  in  best  condition  when  contact  O  is 
constantly  moving  very  slightly. 

Adjustment. — To  increase  amount  of  current,  loosen  the 
check-nuts  A*  at  the  top  of  spring  in  regulator  (Fig.  86),  and 
weaken  tension  of  spring  S\  to  decrease  current,  draw  up 
spring.  Drawing  up  spring  draws  up  regulator. 

Binding-post  P1  on  top  of  box  is  positive  terminal  of 
dynamo  system,  to  which  must  be  connected  the  positive  or 
upper  carbon  side  of  the  lamp  circuit.  A  series  incandescent 
lamp  placed  directly  in  the  circuit  above  the  box,  to  light  it 
up  and  serve  as  a  pilot-lamp  to  indicate  trouble  on  the 
circuit,  is  convenient. 

Field  Switch. — This  is  screwed  in  place  on  the  two  bars 
next  above  the  commutator,  tapped  holes  being  provided. 
The  handle  goes  up  and  the  terminal  wires  will  be  found 
directly  underneath,  ready  for  attaching. 


Dynamos  and  Motors. 


177 


FIG.  86. — DIAGRAM  COMPLETE  ARC  CIRCUIT. 


FIG.  87. — ARC-DYNAMO  ARMATURE,  RING  TYPE. 


178  Practical  Management  of 

Ring  Armatures. — The  new  Gramme  ring  armatures 
now  made  for  the  most  common  sizes  are  interchangeable 
with  the  old  style. 

The  iron  core  is  made  solid  except  at  one  point,  where 
there  is  a  removable  wedge  "to  permit  replacing  the  coils.  Its 
position  is  indicated  by  a  W  stamped  on  the  hub  of  the 
loose  spider.  These  coils  are  wound  on  a  form  and  slipped 
into  place,  and  the  wedge  inserted  and  insulated ;  and  after 
properly  spacing  the  coils,  the  gun-metal  spider  is  clamped 
in  position,  the  shaft  inserted,  and  the  bands  wound  on  after 
wooden  spacing-blocks  have  been  placed  between  the  coils. 

To  replace  a  coil,  cut  the  brass  wire  bands  with  a  hack 
saw ;  disconnect  the  damaged  coil ;  remove  the  lead  wires 
and  wooden  disks  at  either  end  of  the  armature.  These  disks 
are  held  in  position  by  set-screws  in  the  pieces  of  brass  let 
into  their  sides.  Remove  the  bolts  from  the  spider ;  with  a 
drift  remove  the  key  from  the  spider  and  shaft ;  take  off  the 
loose  spider  at  the  commutator  end.  The  fixed  spider  at  the 
pulley  end  is  held  in  place  on  the  shaft  by  a  pin  ;  by  driving 
on  the  commutator  end  of  the  shaft  this  spider  and  the  shaft 
may  be  removed,  and  the  loose  spider  in  the  interior  of  the 


FIG.  88. — COIL  WITH  LONG  TERMINAL  FOR  CROSS  CONNECTION. 

ring  can  them  be  removed  by  striking  it  with  a  block  of  wood. 
Next  remove  the  wooden  wedges,  move  the  coils  around 
until  the  wedge  is  uncovered,  cut  away  the  core  insulation 
for  3J  inches  both  inside  and  outside  the  ring  over  the  wedge  ; 
drive  it  out  carefully,  and  remove  the  bad  coil.  After  re- 
placing with  a  good  coil,  the  operation  is  reversed  ;  reinsulate 
the  wedge  and  its  surroundings  carefully. 


Dynamos  and  Motors. 


179 


The  insulation  used  is  as  follows,  and  should  break  joints: 
Commencing  at  the  core,  two  layers  paper  and  a  layer  each 
of  the  following  in  the  order  named  :  canvas,  mica,  tape, 
canvas,  tape,  and  paper. 

Before  starting  dynamo,  try  all  screws  and  connections  ; 
see  that  brushes  are  carefully  and  correctly  set  ;  carefully 
clean  all  insulation  that  can  be  gotten  at,  especially  the  hard- 
rubber  parts  of  commutator,  and  the  hard-rubber  washers 
on  both  front  and  back  of  binding  and  terminal  posts. 

A  good  test  of  the  carefulness  of  the  cleaner  is  to  try 
the  cleanliness  of  washers  on  back  end  of  posts  P  and  N. 
In"  starting  the  dynamo,  see  that  the  field  switch  is  closed, 
arrange  the  switchboard  so  that  a  circuit  is  attached  to 
the  machine ;  then  lift  the  regulator  to  a  point  about  right 
to  catch  the  load  and  open  the  field  switch  ;  watch  the 
machine  until  the  regulator  settles  well  to  its  work. 

Caution. — Always  lift  regulator  by  taking  hold  just  under 
dash-pot ;  never  lift  by  the  end  of  the  lever,  as  in  a  short 
time  it  will  be  bent  enough  to  destroy  all  cut-out  adjust- 
ments. 


BLACK  MARK 
ON  ARMATURE 


DRUM  ARMATURE 


RING  ARMATURE 


To  change  a  right-hand  T.  H.  arc  dynamo  to  run  left- 
handed,  the  following  special  left-handed  parts  must  be 
ordered  :  Back  plate,  air  blast,  air-blast  jets,  yokes,  brush 
holders.  The  regulator,  J/,,Fig.  73,  and  the  vulcanite  block 
which  carries  binding  post,  P2,  must  be  taken  off  and  fast- 
ened to  the  opposite  field,  for  which  new  holes  must  be 
drilled  and  tapped,  the  regulator  being  itself  reassembled 


i8o  Practical  Management  of 

with  supporting  arm  on  opposite  side.  In  M,  L,  K,  H,  and 
£12  dynamos,  a  new  air-blast  key  must  be  fitted  in  shaft  60° 
from  former  position.  In  MD  and  LD  machines  this  is  not 
necessary.  The  controller  will  now  be  on  negative  side  of 
machine,  and  if  it  is  desired  to  make  this  the  positive  side, 
fields  must  be  remagnetized  so  that  right  field  will  attract 
north  end  of  compass  needle,  but  then  the  line  terminals 
must  be  reversed.  The  cut-out  is  set  precisely  as  with  right- 
hand  machines.  To  set  commutator,  set  brushes  accurately 
to  gauge,  turn  armature  so  that  lead  wire  of  No.  I  coil  is 
on  top,  then  turn  armature  in  direction  in  which  it  is  to 
rotate  until  coil  No.  I  just  disappears  under  right  field  ;  then 
set  commutator  with  segment  No.  I  corresponding  in  posi- 
tion with  coil  No.  i,  and  set  the  lead  on  segment  3  and 
fasten  commutator. 


Dynam os  and  Motors.  1 8 1 


CHAPTER  XXX. 

THOMSON-HOUSTON   ARC   DYNAMO. 
LOCALIZATION   AND   REMEDY   OF   TROUBLES. 

Sparking  at  Commutator  is  a  small  flame  appearing 
at  the  ends  of  the  brushes,  which  is  long  or  short,  purplish 
or  yellow,  according  as  it  is  normal  or  abnormal. 

Normal  spark  is  on  forward  brushes  ;  its  character  denotes 
condition  of  dynamos;  it  varies  a  trifle  with  different 
machines,  but  in  general,  with  full  load  and  rated  speed, 
should  be  about  T3T  inch  long,  and  purplish  in  color.  As  load 
decreases,  length  of  spark  increases.  It  does  no  harm,  and 
its  adjustment  is  given  on  page  169. 

Flashing  at  Commutator  is  a  sudden  violent  flash  of 
flame  about  the  commutator,  immediately  followed  by  a 
momentary  lowering  of  the  regulator  to  catch  the  current 
again.  A  flash  acts  as  a  momentary  short-circuit  of  the 
armature,  which  stops  generating  current  until  caught  up  by 
the  regulator. 

FLASHING  OR   SPARKING. 

1.  Cause. — Air-blast  loose  on  back-plate. 

Symptom. — Feels  loose  to  hand  ;  bubbles  of  air  and 
oil  appear  at  joint  with  back-plate;  air-jet  disarranged. 

Remedy. — Loosen  bolts  A,  Fig.  82  ;  adjust  as  per  direc- 
tions on  page  172,  and  tighten  bolts. 

2.  Cause. — Screens  in  air -blast  stopped  ivith  dirt. 
Symptom. — Decreased  power  of  air-jet. 

Remedy. — Clean  screens  and  free  the  openings. 
Note. — Never  leave  screens  out  altogether. 

UNIVERSITY 


1 82  Practical  Management  of 

3.  Cause. —  Wings  in  air-blast  stick. 

Symptom. — Same  as  Cause  2.  Examination  may  show 
wings  to  be  gummed  and  sticky  from  bad  oil.  Wings  in 
older  machines  sometimes  stick  from  the  vacuum  on  lower 
edge  of  wing  ;  new  dynamos  have  grooves  filed  in  this  edge 
to  prevent  formation  of  a  vacuum. 

Remedy. — Thoroughly  clean  wings  and  slots ;  file  grooves 
in  bottom  edge  of  wings  if  there  are  none. 

4.  Cause. —  Wings  in  air-blast  reversed. 

Symptom. — Same  as  Cause  2.  Examination  shows 
wings  are  reversed. 

Remedy. — Reverse  the  wings. 

5.  Cause. — Jets  stopped  with  dirt  or  orifice  jammed. 
Symptom. — Same  as  Cause  2. 

Remedy. — Clean  thoroughly ;  open  and  clear  slot  with 
knife-blade. 

6.  Cause. — Air-blast  set  too  far  to  the  left,  or  jets  not  ad- 
justed correctly. 

Symptom. — Continued  flashing  at  short  irregular  inter- 
vals, with  no  apparent  cause;  spark  somewhat  irregular; 
weak  jet  of  air;  jets  out  of  position. 

Remedy. — Loosen  bolts  A,  Figs.  82-85;  readjust  as  per 
directions  on  page  172,  and  tighten  bolts. 

7.  Cause. — Key  or  slot  in  air -blast  worn  or  changed. 
Symptom. — Same  as  Cause  6. 

Remedy. — If  slot  in  blower  spider  is  worn,  have  new 
slot  cut  120°  from  old,  or  have  original  slot  repaired  by 
fitting  a  piece  of  steel  into  the  worn  edge.  If  key  is  badly 
worn,  replace  it  with  new  one. 

8.  Cause. — Commutator  not  set  correctly. 
Symptom.— Bad  flashing;  machine  may  practically  refuse 

to  generate   if   but  slightly  out  of  adjustment  ;  flashing  at 
irregular  intervals. 


Dynamos  and  Motors.  "  183 

Remedy. — When  running,  readjust  cut-out  by  the  slide 
on  yoke,  using  insulated  wrench  and  tools ;  reset  commutator 
as  per  directions,  page  167. 

9.  Cause. — Regulator  yokes  and  connections  not  working 
freely. 

Symptom. — Variation  in  size  of  spark;  movement  of 
yokes  stopped  at  intervals  ;  several  flashes  in, quick  succession. 

Remedy. — Remove  connection  of  yokes  to  regulator^ 
arm  ;  locate  and  remove  the  obstruction  to  their  movement. 

10.  Cause. — Contacts  in  wall-controller  bad. 

Symptom. — A  tendency  of  the  regulator  armature  to 
stay  up,  causing  violent  flashing  as  soon  as  the  spark  disap- 
pears at  the  top  brush  ;  will  flash  two  or  three  times  in  quick 
succession. 

Remedy. — Clean  the  contacts  with  sand-paper  or  file. 

11.  Cause. — Dynamo  overloaded. 

Symptom. — Regulator  down  on  stop ;  spark  will  gradu- 
ally shorten  and  disappear ;  then  a  violent  flash. 

Remedy. — Remove  part  of  load. 

Note. — A  bad  joint  or  contact  in  the  line  will  produce 
same  effect  as  overload. 

12.  Cause. — Dynamo  not  up  to  speed  to  carry  the  load. 
Symptom. — Same  as  Cause  u. 

Remedy. — Speed  up,  or  remove  part  of  load. 

13.  Cause. —  Too  much   oil  used  in  blower  and  on  com- 
mutator. 

Symptom. — Bad  sparking  at  commutator  on  all  brushes, 
followed  at  irregular  intervals  by  weak  flashing. 

Remedy. — Decrease  supply  of  oil,  and  remove  surplus 
from  commutator  with  small  piece  of  canvas  folded. 

14.  Cause. — Animal  or  other  bad  oil. 

Symptom. — Same  as  No.  13,  and  a  gummy  appearance 


184  Practical  Management  of 

of  commutator;  brushes  burn  and  spark,  followed  by  flash- 
ing as  in  No.  13. 

Remedy. — Change  oil  at  once  ;  clean  all  parts  of  blower 
and  commutator  when  shut  down. 

15.  Cause. — Lint  from  wiping  rag. 
Symptom. — Flashing  with  no  apparent  reason. 
Remedy. — Stop  machine  ;  clean  commutator  thoroughly. 

1 6.  Cause. — Dash-pot  too  weak  or  too  stiff. 

Symptom. — Same  as  No.  10;  regulator  works  very  slowly 
if  too  stiff,  and  if  too  weak  will  move  too  far,  thus  causing  a 
surging  of  spark  and  current. 

Remedy. — If  too  stiff,  thin  down  glycerine  with  a  little 
water  ;  if  too  weak,  swedge  out  the  plunger  a  trifle  by  squeez- 
ing it  in  a  vise. 

17.  Cause. — Current  surging. 

Symptom. — Current  varies  more  than  usual,  as  shown  by 
ammeter;  contacts  of  wall-controller  stay  apart  for  long 
period  or  together  for  the  same  time ;  regulator  has  much 
more  than  usual  movement,  and  gradually  rises  beyond  limits 
of  standard  current ;  spark  disappears,  and  is  followed  by 
violent  flashing  two  or  three  times  in  quick  succession ;  after 
which  regulator  settles  back  and  same  effect  is  repeated 
after  a  short  time.  This  rarely  happens  in  any  but  dyna- 
mos newly  set  up,  and  is  generally  due  to  carelessly  adjusted 
commutator  or  to  too  wide  separation  of  controller  contacts. 
The  same  symptoms  in  an  old  dynamo  generally  indicate 
that  the  commutator  has  moved  back. 

Remedy. — See  that  the  dash-pot,  regulator,  yokes,  and 
all  moving  parts  are  free. 

1 8.  Cause. — Dirt  on  insulation  of  machine,  forming  con- 
tact. 

Symptom. — Flashing;  arcing  across  insulating  washers 
or  insulating  plates  on  commutator,  inspection  shows  copper 
dust. 


Dynamos  and  Motors.  185 

Remedy. — Thoroughly  clean  the  parts  and  coat  with 
shellac. 

19.  Cause. — False  contact  in  armature. 

Symptom. — Violent  flash,  then  a  spark  much  longer 
than  usual  appears,  arching  over  the  regular  spark  and 
lengthening  and  shortening  at  intervals  ;  it  is  from  ^  to  f 
inch  long  from  the  tip  of  the  forward  brush.  It  is  much  dif- 
ferent in  appearance  from  the  regular  spark,  and  is  a  sure 
indication  of  a  short  circuit  in  a  coil,  which  will  burn  out 
if  left  running  long  enough ;  regulator  sometimes  works 
normally,  but  generally  settles  down  upon  stop. 

Remedy. — Stop  the  machine;  locate  the  damaged  coil 
by  its  extra  heat ;  rewind. 

20.  Cause. — Break  in  armature  circuit. 

Symptom. — Flashing  and  violent  sparking  at  commu- 
tator. 

Remedy. — Stop  dynamo,  remove  brushes,  and  test  with 
magneto,  from  each  segment  to  back  connection  ;  locate 
break,  and  rewind  as  much  as  is  necessary. 

21.  Cause. — Swinging  contact  on  line  ;  cutting  load,  i.e., 
part  of  circuit  on  and  off. 

Symptom. — Violent  flashing,  at  comparatively  regular  in- 
tervals ;  regulator  rapidly  falling  to  catch  load,  followed  by 
violent  spark  and  rise  of  regulator. 

Remedy. — Locate  the  swinging  contact  and  remove  it. 

22.  Cause. — Brushes  not  accurately  adjusted  by  gauge. 
Symptom. — Bad  sparking,  with  an  occasional  flash. 

Remedy. — Test  each  brush  with  gauge ;  correct  any 
found  out  of  adjustment. 

ADDITIONAL  CAUSES   OF  ABNORMAL   SPARKING  ONLY. 

23.  Cause. — Brush  not  set  accurately  ;  clamp  loose ;  finger 
of  brush  bent  out  of  place. 


1 86  Practical  Management  of 

Symptom. — Violent  sparking  on  the  brush  affected  ;  ex- 
amination shows  finger  bent  under  so  as  to  disarrange  all 
commutator^  adjustments ;  sometimes  caused  by  turning 
armature  backward. 


FIG.  89. — ARC  DYNAMO  BRUSH. 

Remedy. — Straighten  out  the  brush  (Fig.  89)  and  re- 
place by  gauge  ;  tighten  brush  clamp,  after  testing  length  of 
brush  with  gauge.  In  case  this  does  not  stop  sparking,  stop 
machine  and  examine  all  commutator  adjustments. 

24.  Cause. — Blower-jets  worn  so  that  they  do  not  fit  hole 
in  body  of  blower. 

Symptom. — Leakage  of  air  can  be  felt  in  front  of  jet- 
tube  ;  oil  and  air  bubbles  appear  around  jet-tube ;  air-jet 
weakened. 

Remedy. — Get  new  jets  at  earliest  opportunity.  Remedy 
temporarily  by  wrapping  tube  of  air-jet  with  tape  or  paper. 

25.  Cause. — Rubber  thimble  between  tube  ana  jet  bent  out 
of  line  by  heat. 

Symptom. — Jer  sets  crooked ;  commutator  sparks  and 
flashes  because  jet  of  air  is  not  delivered  squarely. 

Remedy. — Soften  the  hard-rubber  thimble  over  flame, 
and  bend  back  into  place. 

26.  Cause. — Copper  finger  contacts,  inside  of  sliding  con- 
nection, between  side  brushes,  worn  with  use. 

Symptom. — Bad  sparking  on  the  -primary  brush,  which 
disappears  when  the  two- brushes  are  short-circuited  with  a 
piece  of  wire ;  flat  groove  across  face  of  each  segment,  caus- 
ing brushes  to  chatter. 

Remedy. — Examine  the  parts  ;  bend  copper  fingers  out 
to  make  good  contact,  or  replace  with  new  ones ;  see  that 
interior  of  barrel  is  clean. 


Dynamos  and  Motors.  187 

. — Any  point  of  bad  contact  in  or  about  this  con- 
nection will  give  same  symptoms. 

27.  Cause. — Loose  commutator  segments,   causing  disar- 
rangement of  adjustments,  or  slightly  loose  lead-wires  ;  if  very 
loose,  will  stop  current  entirely. 

Symptom. — Inspection  and  feeling  show  loose  parts. 

Remedy. — See  that  all  screws  and  other  parts  about 
commutator  are  tight  before  starting. 

28.  Cause. — Lead-wires  connected  to  wrong  segments  of 
commutator.      This  sometimes  happens  when  from  long  use  the 
distinguishing  colors  of  the  wires  cannot  be  seen*,  and  they  are 
misplaced  when  commutator  is  removed  for  any  reason. 

Symptom. — Dynamo  generates  little  if  any  current, 
while  a  violent  spark  appears  at  brushes  and  surges  back  and 
forth  ;  occasionally  breaks  altogether  and  starts  over  again  ; 
regulator  remains  on  stop,  as  standard  current  is  not  gen- 
erated. This  symptom  resembles  No.  19,  although  with 
contact  in  armature  the  regulator  may  be  working  almost 
normally.  ' 

Remedy. — Stop  the  dynamo,  examine,  and  reconnect 
leads. 

29.  Cause. —  Too  much  oil,  or  oil  of  bad  quality  on  blower 
and  commutator. 

Symptom. — Large  sparks  at  primary  or  side  brushes ; 
top  spark  of  yellow  color ;  all  brushes  wear  away  at  tips,  re- 
quiring retrimming  during  a  run. 

Remedy. — Shut  off  oil  at  blower-oiler  and  wipe  commu- 
tator with  canvas ;  if  quality  is  bad,  change  at  once. 

30.  Cause. — Brushes  ragged  through  lack  of  trimming  or 
rapid  wear. 

Symptom. — Brushes   grow   thin   at  the   ends   and    look 
ragged. 

Remedy. — Trim  brushes  off  square,  and  far  enough  back 
from  ends  to  have  a  good  bearing-surface. 


1 88  Practical  Management  of 

3 1 .  Cause. — -^Commutator  grooved  or  rough. 

Symptom.  (See  No.  26.)  Sparking  and  movement  at 
all  brushes ;  feels  rough  to  touch  ;  brushes  chatter. 

Remedy. — Remove  segments  (Fig.  90),  and  turn  up  the 
surface  by  placing  them  on  a  "  jig," 
made  for  the  purpose ;  or,  if  but  thin 
cut  is  needed,  remove  whole  commu- 
tator and  turn  them  while  in  position. 
Brushes  should  have  unlike  number  of 
fingers  to  give  smooth  commutator. 

Note. — Segments  should  not  be  used  FIG.  90. -SEGMENT  OF 
if  thinner  than  one-eighth  inch,  as  slot  is      ARC  COMMUTATOR. 
widened  too  much  then  ;  slot  should  be  about  ^  inch  wide. 

32.  Cause. —  Too  much  current  being  generated. 

Symptom. — Bad  sparking;  ammeter  shows  too  much 
current. 

Remedy. — Examine  connections  to  wall-controller,  which 
may  be  broken  or  reversed ;  examine  controller  for  trouble ; 
see  that  spring  5  is  properly  adjusted;  if  broken,  much 
heavier  current  will  be  needed  to  lift  magnet  cores 'and  break 
contact. 

HEATING  OF    ARMATURE.     (See  page  136.) 
SPECIAL    CAUSES. 

i.  Cause. — Slow  speed. 

Symptom. — Less  than  usual  amount  of  air  thrown  off, 
as  decrease  of  speed  decreases  ventilation  ;  air  thrown  off 
very  hot ;  air-jet  weak,  and  sparking  worse  than  usual  in 
consequence. 

Remedy. — Speed  up  to  maker's  standard. 

2o  Cause. —  Underload,  which  to  a  trifling  extent  increases 
ampereage. 

Symptom. — Violent  spark  at  commutator  top  brush, 
looping  down  through  slot  between  segments ;  regulator 
high  up. 

Remedy. — Shift  load  to  another  machine,  or  put  on 
more  load  if  obliged  to  run  for  any  length  of  time. 


Dynamos  and  Motors.  189 

Note.  —  Although  this  dynamo  is  capable  of  being  run 
on  short-circuit  for  hours,  it  is  not  desirable  to  run  on  less 
than  one-third  full  load. 

3-  Cause.  —  Increase  of  current  above  normal  standard. 

Symptom.  —  Air  from  armature  much  hotter  than  usual  ; 
bad  sparking  at  commutator;  ammeter  shows  too  much 
current.  •, 

Remedy.  —  To  cool  machine  down,  cut  off  current  and 
run  it  with  no  current  for  a  time  ;  find  cause  for  increase  of 
current  (see  Abnormal  Sparking,  Cause  32),  and  remove. 

Heating  of  Field-magnets.     See  page  138. 

Heating  of  Bearings.     See  page  140. 

Noise.     See  page  145. 

Special  noise  features  of  this  machine  are  the  spark  and 
the  air-blast  jets,  which  increase  somewhat  as  the  load  de- 
creases. 

Note.  —  In  case  of  sudden  increase  of  noise,  examine 
dynamo  immediately. 

Dynamo  Fails  to  Generate.     See  page  155. 

REVERSAL   OF  POLARITY. 

Cause.  —  By  lightning  striking  line,  or  contact  ivith  other 
circuits. 

Symptom.  —  Arc  lamps  burning  "  upside  down  ;  "  i.e., 
with  bottom  carbon  positive  and  light  directed  upward  in- 
stead of  down  ;  if  not  soon  changed,  bottom  carbon-holders 
will  be  destroyed. 

Remedy.  —  If  no  other  dynamo  is  at  hand,  reverse  either 
circuit  or  machine's  terminal  wires  at  switchboard.  When 
another  dynamo  can  be  had,  short-circuit  the  armature  of 
the  reversed  machine  either  with  the  field  switch  or  by  a 
wire  from  terminal  post  A  to  post  A'  ;  attach  the  circuit 
from  the  live  machine  to  the  binding-posts  P  and  A7"  of  the 
reversed  machine,  noting  that  the  positive  terminal  of  one 
is  attached  to  negative  terminal  of  the  other;  turn  on  cur- 
rent an  instant,  and  the  polarity  will  be  corrected. 

Caution.  —  Never  attempt  to  do  this  while  armature  is 
revolving. 


TT'NrTVF.-RQTT-v 


1 90  Practical  Management  of 


CHAPTER  XXXI. 
BRUSH   ARC   DYNAMO. 

Setting  Up. — Set  the  dynamo  so  that  its  base  is  about 
one  foot  above  the  floor,  upon  a  wooden  frame  or  founda- 
tion timbers  which  are  oiled  or  varnished  and  firmly  fas- 
tened to  the  floor  or  to  a  brick  foundation.  Unpack  the 
"  dial  "  or  regulator  carefully,  and  lay  it  down  flat.  Remove 
all  the  blocks  which  hold  the  parts  in  place  during  transpor 
tation.  Take  off  the  slate  over  the  carbon  piles,  and  blow 
out  the  carbon  dust  with  a  bellows.  Replace  the  slate 
cover  and  screw  it  down,  but  leave  a  slight  play  under  the 
screw-heads.  Then  mount  the  dial  on  the  wall  or  upon  a 
stand  near  the  dynamo,  and  hang  it  on  hinges  or  arrange  it 
so  that  its  lower  end  can  be  swung  outwards  a  little,  in  order 
that  the  slate  cover  can  be  taken  off  and  the  carbon  piles 
examined  and  adjusted  without  danger  of  their  falling  out. 

To  start  a  new  machine  for  the  first  time,  connect  the 
two  binding-posts  on  top  of  the  dial  to  the  small  posts  of 
the  dynamo  between  the  large  binding-posts  of  the  ma- 
chine. Connect  the  left-hand  post  at  the  bottom  of  the 
dial  to  the  positive  post  of  the  dynamo,  and  the  right-hand 
post  of  the  dial  to  the  negative  post  on  the  machine.  In 
other  words,  short-circuit  the  dynamo,  with  the  dial  alone 
in  circuit,  no  lamps  being  connected.  If  there  be  sufficient 
time,  it  is  well  to  run  a  new  dynamo  in  this  way  several 
hours.  The  dynamo  will  run  short-circuited  as  long  as  de- 
sired without  trouble  or  danger.  Take  care  to  have  the 
cleaner  on  hand  when  dynamo  is  shut  down  ;  take  off  the 
brushes  and  all  the  copper  segments  immediately,  and  wipe 
the  surfaces  of  the  brass  and  copper  segments  thoroughly 
with  a  dry  rag.  Remove  the  thin  film  of  shellac  which  will  be 
found  on  the  brass  and  copper  surfaces,  as  it  might  get  upon 
the  commutator  and  cause  the  machine  to  flash.  Pay  par- 
ticular attention  to  the  ends  of  the  commutator.  After 


UNIVERSITY 


Dynamos  and 


* 


TERSITY  l 

A  L I  FOR^i!^^^^ 





FIG.  91. — BRUSH  ARC  DYNAMO. 


1 9 2  -P*  octical  Management  of 

cleaning  the  commutator,  incline  the  dial  backward,  take  off 
the  slate  over  the  carbon  piles  and  wipe  the  moisture  from 
the  slate  frame,  etc.,  and  in  replacing  the  slate  leave  the 
screws  somewhat  loose.  After  the  machine  is  cooled  off, 
tighten  up  all  contacts  and  connections. 

In  running  the  dynamo  iipon  the  regular  circuit,  it  is  good 
practice  to  start  with  a  long  spark,  about  \  inch,  especially 
in  the  case  of  a  cold  circuit.  When  the  carbon  points  become 
hot  and  the  lamps  are  up  to  full  arcs,  the  spark  will  be 
shorter — about  \  inch.  Make  it  a  point  to  look  at  the  posi- 
tion of  brushes  after  starting  the  circuit — say  at  the  end  of 
five  minutes.  To  oil  the  commutator,  put  a  very  few  drops 
of  oil  upon  one  side  or  end  of  a  piece  of  duck  or  felt,  and 
apply  it  "  right  in  the  spark."  If  the  oil  is  put  on  at  some 
distance  from  the  end  of  the  brush,  the  machine  is  liable  to 
flash.  A  new  wooden  block  commutator  does  not  require 
as  much  oil  as  an  old  one.  Always  have  a  dry  rag  at  hand, 
and  wipe  the  commutator  with  it  two  or  three  times  during 
the  evening.  Use  very  little  oil  on  the  commutator,  but 
apply  it  often. 

Care  and  Management. — Provide  your  cleaner  or  wiper 
with  some  cotton  cloth  and  a  small  hardwood  stick,  6  inches 
long  and  I  inch  square,  tapering  down  at  one  end  to  I  inch 
wide  and  £  inch  thick.  The  cleaning  should  begin  as  soon 
as  the  machine  shuts  down,  ten  minutes'  work  while  the  ma- 
chine is  hot  being  better  than  forty  minutes  the  next  day. 
Clean  the  spaces  between  the  commutator  segments  thor- 
oughly, using  the  cotton  cloth  and  the  stick.  Take  care  to 
have  all  the  copper  dust  wiped  off,  giving  special  attention 
to  the  ends  of  the  commutator.  The  front  end  may  be- 
come connected  to  the  bushing  if  the  dust  is  not  removed, 
and  the  back  end  will  short-circuit  two  commutator  wires  if 
the  wooden  surface  is  not  kept  free  from  oil  and  copper 
dust.  A  great  deal  of  trouble  will  be  saved  if  care  is  taken 
in  cleaning  the  places  where  the  commutator  wires  and 
shaft  wires  are  connected. 

To  prevent  the  commutator  from  becoming  rough  and 
uneven,  polish  it  with  fine  sand-paper  when  the  dynamo  is 
running  at  full  speed.  Use  a  piece  of  wood  12  inches 
long,  3  inches  wide,  and  -J  inch  thick  to  hold  the  sand- 


Dynamos  and  Motors.  193 

paper  against  the  commutator.  This  treatment  twice  a 
week  will  keep  the  commutator  in  good  condition,  and  is 
much  better  than  cleaning  with  files  or  emery. 

When  using  blowers  or  bellows  to  remove  dust  from  ar- 
matures, there  should  be  an  exhaust-fan  arranged  to  draw 
the  dust  out  of  the  room  while  the  armatures  are  being 
cleaned.  If  the  dust  is  not  drawn  out  of  the  room,  blowing 
out  the  armature  does  not  do  much  good,  as,  the  dust  will 
settle  on  the  other  machines. 

To  get  sufficient  pressure  of  the  brush  upon  the  com- 
mutator, it  is  better  to  use  a  light  "  pressure-brush  "  over  the 
regular  copper  brush  than  to  attempt  to  bend  the  regular 
brush  to  increase  its  pressure.  Adjust  the  brushes  so  that 
they  are  just  long  enough  to  bear  on  the  commutator  at  a 
point  about  \  to  J  inch  from  their  extreme  ends. 

Dynamos  are  ordinarily  made  to  run  right-handed,  but 
they  may  be  ordered  for  left-handed  running,  if  desired.  If 
it  becomes  necessary  to  change  the  direction  of  rotation  of 
a  machine,  it  may  be  accomplished  by  simply  reversing  the 
connections  of  the  field,  and  changing  the  lead  of  the  com- 
mutator, which  should  always  be  set  about  \  inch  forward, 
that  is,  in  the  direction  of  rotation.  Hence  in  reversing  a 
machine  the  position  of  the  commutator  should  be  changed 
about  inch. 


TROUBLES  AND   REMEDIES. 

The  Brush  arc  dynamo  is  simple,  and  not  very  subject  to 
troubles  ;  but  the  following  are  among  the  principal  faults 
which  might  require  attention. 

The  dial  or  regulator  may  get  out  of  adjustment  in  one 
of  the  following  ways  : 

1.  The  dial  may  not  "  take  hold  "  at  the  proper  point  ;  that 
is,  either  too  much  or  too  little  current  in  the  main  circuit 
may  be  required  before  the  solenoid  and  movable  lever  act 
to  press  together  the  piles  of  carbon  plates  which  shunt  more 
or  less  current  from  the  field  to  regulate  the  machine. 

2.  The  action  of  the  dial  may  not  be  steady  ;  that  is,  the 
resistance  of  the  carbon  piles  may  not  decrease  uniformly, 
as  the  pressure  upon  them  is  increased  by  the  pull  of  the 


1 94  Practical  Management  of 

solenoid.  This  is  ordinarily  caused  by  the  relative  length  of 
the  varr'ous  piles  not  being  right  with  respect  to  each  other. 
For  example,  the  pressure  may  be  exerted  only  upon  the 
middle  pile  or  upon  the  two  end  piles,  instead  of  being 
gradually  and  successively  applied. 

This  trouble  and  the  previous  one  are  overcome  by  care- 
fully adjusting  the  dial  which,  when  properly  set,  will  regu- 
late so  effectively  that  any  number  of  lamps  from  one  to 
full  load  may  be  cut  in  or  out  without  any  considerable 
change  in  the  current  strength. 

3.  Falling  off  in  voltage.     Sometimes  the  ability  of  a  ma- 
chine to  operate  lamps  decreases  gradually  after  being  used 
a  long  time,  owing  to  the  insulation  of  the  armature  bobbins 
being  charred   inside,  which  has  the  effect  of  cutting  out 
some  of  the   turns  of  wire,   and   of  course  decreases    the 
voltage  of  the  machine.     This  charring  may  extend  until 
only  one  or  two  of  the  outside  layers  are  left  intact,  and 
although  the  appearance  of  the  coils  may  be  all  right,  most 
of  the  coils  are   actually  cut  out  or  connected  together  by 
the  burnt  insulation.     In  such  a  case  the  bobbins  should  of 
course  be  rewound. 

4.  If  one  bobbin  of  an  armature  is  burnt  out,  the  machine 
may  be  run  temporarily  in  an  emergency  by  cutting  out  or 
"  connecting  by  "  the  opposite  one,  care  being  taken  to  open 
the  circuit  of  these  coils,  so  that  they  are  not  short-circuited. 

In  a  similar  manner,  the  capacity  of  a  machine  may  be 
reduced  to  f  or  £,  respectively,  by  cutting  out  two  opposite 
bobbins,  or  four  alternate  ones. 

5.  Flashing.     If  this  occurs  at  regular  intervals  of  about 
8  minutes,  it  is  usually  caused  by  the  fine-wire  circuit  in  some 
lamp  or  lamps  being  open,  so  the  carbons  cannot  be  fed 
down.     As  the  burning  away  of  the  carbons  continues,  the 
resistance  of  the  arc  increases  and  the  current  as  shown  by 
the  ammeter  (Fig.  92)  decreases ;  the  magnetization  of  the 
field  diminishes,  changing  the  line  of  commutation  in  the 
armature ;  the  spark  at  the   commutator  gets  smaller  and 
smaller  until  the  machine  flashes,  the  carbons  drop  together, 
and  the  same  performance  is  repeated.     As  the  spark  gets 
smaller,  rocking  back  the  brushes  will  postpone  the  flash  for 
a  few  minutes  ;  but  it  can  be  readily  understood  that  the  only 


Dynamos  and  Motors. 


195 


way  to  cure  the  trouble  is  to  locate  the.lamps  that  burn  with 
a  flashing  arc  and  repair  their  fine-wire  shunt  circuits. 

Sometimes  lightning  breaks  the  fine-wire  circuit  of  several 
lamps  on  one  circuit.     As  long  as  one  such  lamp  is  in  the 


FIG.  92. — BRUSH  AMMETER. 

circuit  the  dynamo  will  flash.  Anything  that  causes  the 
spark  to  get  too  short  on  the  commutators,  like  throwing 
on  more  load  or  slowing  of  speed,  will  cause  a  flash.  On 
large  dynamos  running  old-style  Brush  arc  lamps,  some- 
times after  a  flash  the  machine  will  not  start  the  lamps  for 
some  minutes,  unless  the  switch  on  the  machine  board  is 
closed  and  again  opened.  This  is  caused  by  the  glycerine 
in  some  or  all  of  the  lamps  being  too  thick,  and  the  fine-wire 


196  Practical  Manage  merit  of 

circuit  of  some  of  the  lamps  reversing  the  polarity  of  the 
lamp  armature  and  holding  the  carbons  apart,  thus  prevent- 
ing the  circuit  closing. 

6.  Sparking  at  the  commutator  of  Brush  arc  machines  is 
legitimate,  but  should  not  be  allowed  to  get  long  enough  to 
permit  flashing.    A  spark  about  \  inch  long  is  right.    If  the 
commutator  is  allowed  to  get  rough  or  out  of  round  or  dirty, 
or  the  brushes  do  not  all  press  fairly  upon  it,  a  damaging 
spark  and  trouble  are  likely  to  follow. 

7.  Failure  to  generate  is  sometimes  caused  by  the  line 
being  open,  in  which  case  test  by  momentarily  short-circuit- 
ing across  the  terminals  of  the  dynamo  ;  if  there  is  yet  no 
current,  then  test  the  circuits  of  the  dynamo  either  with  a 
magneto  or  the  current  of  another  dynamo,  as  it  is  likely 
there  is  an  open  circuit  in  the  dynamo  itself,  or  at  least  a  bad 
connection.     After  using  a  current  from  another  source  in 
testing  a  dynamo,  always  be  sure  to  see  that  the  polarity  of 
dynamos  has  not  been  changed  ;  if  it  has  been,  change   it 
back,  or  transpose  the  line  wires  at  the  dynamo  terminals. 

8.  Heating  of  tips  of  field-magnet  poles.     The  two  upper 
and  the  two  lower  pole-piece  tips,  that  is,  those  which  the 
armature    moves  away  from,  may  become  heated.     This  is 
not  serious,  and  is  due  merely  to  local  or  Foucault  currents 
in  the  iron  itself. 

9.  The  field  coils  on  one  side  may  be  warmer  than  those  on 
the   other   in    an    old-style    dynamo    for    !2OO-candle-power 
lamps,  because  the  regulator  only  shunts  one  half  of  the  field. 
With  partial  load  the   shunted  side  is  considerably  cooler 
than  the  other.     This  does  no  harm,  but  sometimes  causes 
surprise. 


Dynamos  and  Motors. 


197 


CHAPTER   XXXII. 

FORT  WAYNE   (WOOD),  SPERRY,  AND   EXCELSIOR   ARC 

DYNAMOS. 

THESE  are  all  regular,  closed-coil  ring-armature  machines, 
such  as  are  treated  throughout  this  book,  and  therefore 
require  no  special  directions,  except  for  the  regulators.  The 
regulators  are  mechanical  devices  for  moving  the  brushes 
back  and  forth  to  keep  the  current  constant  in  spite  of  varia- 
tions in  the  number  of  lamps  or  other  changes  in  the  circuit. 

Directions  for  the  Wood  Machine. — Observe  strictly  all 
previous  general  directions.  As  it  has  a  closed-coil  armature, 


FIG.  93. — WOOD  DYNAMO,  WITH  STEP-BY-STEP  BRUSH-MOVING  GOVERNOR, 

the  brushes  should  not  spark  at  all,  and  consequently,  with 
good  care  and  brushes  well  trimmed  according  to  directions, 
brushes  should  last  a  year  or  more.  When  facing  the  pulley 
it  must  turn  clockwise  or  right-handed.  The  regulator  acts 


198  Practical  Management  of 

properly  if  the  speed  of  the  machine  is  at  or  above  the 
normal,  but  not  if  it  is  below  when  there  are  many  lights  in 
circuit.  It  must  be  kept  perfectly  clean  and  well  oiled  so  as 
to  move  freely,  and  the  friction-wheel  bearings  must  never  be 
allowed  to  run  dry.  The  armature  should  be  cleaned  once 
a  year  after  removing  the  commutator,  and  the  inside  of  the 
coils  brushed,  particularly  at  commutator  end.  Before  taking 
out  the  armature,  be  sure  to  remove  the  regulator  pinion  to 
prevent  damage,  and  do  not  replace  it  until  the  armature  is 
again  in  position.  Before  removing  commutator,  mark  it  so 
as  to  replace  in  exactly  the  same  position  and  be  careful  to 
keep  commutator-nut  tight  always,  as  the  sections  are  liable 
to  become  loose  by  the  swelling  and  shrinking  of  the  insula- 
tion. The  strength  of  current  can  be  increased  by  tighten- 
ing the  regulator  spring,  and  vice  versa. 

To  see  if  tension  of  this  spring  is  right,  remove  the  t'ric- 
tion-wheel  while  the  dynamo  is  running  and  the  ammeter 
is  indicating  the  proper  current.  Then  by  turning  the  large 
gear  a  little  to  the  right,  so  as  to  increase  the  current  about 
half  an  ampere,  the  magnet  lever  should  move  up  against  the 
stop  ;  and  by  turning  the  gear  to  the  left,  so  as  to  decrease 
the  current  about  half  an  ampere,  the  magnet-lever  should 
be  drawn  down  against  the  under-stop.  When  the  current 
is  standard,  the  lever  should  remain  in  the  middle  position. 

In  adjusting  the  regulator  care  should  be  taken  that  both 
of  the  friction-rollers,  which  revolve  on  the  roller  lever, 
should  be  at  exactly  the  same  distance  from  the  friction- 
wheel,  and  set  in  such  a  manner  that  one  quarter  of  an  inch 
movement  of  the  magnet  lever  would  cause  one  or  other  of 
the  rollers  to  engage  with  the  wheel. 

One  must  also  be  particularly  careful  lo  oil  the  rollers 
from  the  centre  of  the  studs  every  fifteen  or  twenty  minutes, 
for  the  first  week  or  two  after  the  dynamo  is  started,  or  un- 
til such  time  as  they  wear  to  a  perfectly  smooth  bearing. 
The  friction-wheel  is  placed  on  a  movable  stud,  allowing  it 
to  be  moved  to  and  from  the  rollers  in  order  to  compensate 
for  wear.  The  rollers  can  also  be  adjusted  tangentially  to 
the  wheel  by  turning  the  nut  on  the  connecting  link  which 
connects  the  roller  lever  with  the  magnet  lever.  Never 
stop  the  dynamo  without  first  raising  the  magnet  lever — in 


Dynamos  and  Motors.  199 

order  to  bring  the  brushes  to  position  of  minimum  voltage 
— and  throwing  up  the  cam. 

In  starting,  run  the  dynamo  to  speed,  then  remove  the 
cam  and  allow  the  regulator  to  find  proper  pbsition  for  the 
brushes.  In  case  it  becomes  necessary  to  remove  the  auto- 
matic regulator  for  any  cause,  be  particularly  careful  to  put 
every  part  back  in  its  position,  and  see  that  the  yokes  meet 
properly  in  gear ;  that  is,  when  the  clutch  unlocks  at  the 
minimum  point,  the  yokes  should  be  close  together  :  they  will 
then  be  separated  the  proper  distance  the  instant  the  clutch 
unlocks  at  maximum  point.  A  failure  to  comply  with  these 
directions  will  prevent  the  regulator  from  working  properly. 

The  Sperry  machine  is  similar  in  action,  and  the  direc- 
tions are  about  the  same,  with  a  few  changes  to  suit  the 
exact  construction.  The  differences  in  detail  can  readily  be 
understood  upon  inspection. 

The  Excelsior  (Hochhausen)  arc  dynamo  (Fig.  94)  employs 
a  regulator,  comprising  an  electro-magnetic  controller, 
usually  placed  on  a  wall  or  post  near  the  machine,  and  a 
small  electric  motor,  located  on  the  dynamo. 

This  motor  has  a  pinion  upon  its  shaft,  which  meshes 
with  a  semicircular  rack  attached  to  the  rocker-arm  that 
carries  the  main  brushes  (Fig.  95).  When  the  motor  re- 
volves one  way  or  the  other  the  brushes  are  shifted  corre- 
spondingly. The  rocker-arm  is  also  connected  by  a  rod  to 
a  switch  (not  shown),  which  cuts  into  and  out  of  circuit 
sections  of  the  field-winding. 

The  path  of  the  current  and  action  of  the  regulator  is  as 
follows  (Fig.  95): 

Starting  from  the  positive  terminal  of  the  machine  D\ 
the  current  is  led  to  the  binding-post  R*  on  the  wall-con- 
troller and  passes  through  the  magnet  J/into  the  armature- 
lever  A,  through  the  resistances  x,  y,  and  z  to  the  line,  and 
returns  by  the  external  circuit  to  the  negative  terminal  D1. 

The  end  of  the  controller  armature  A  bears  against  two 
contact  points,  C,  C1,  which  are  connected  through  the 
binding-posts  R*  and  R3  on  the  regulator  and  D*  and  D*  on 
the  dynamo  to  the  brushes  of  the  small  regulating  motor 
on  the  machine. 

The   regulating   magnet   M  is    so   adjusted  that  when 


2OO 


Practical  Management  of 


the  normal  current  passes  over  the  line  the  armature  A 
stands  horizontal  and  makes  contact  with  both  points  C,  C\ 
which  are  fixed  at  the  end  of  their  lever.  The  current  enter- 
ing the  armature  A  from  the  magnets  M,  therefore,  be- 
sides passing  to  line  through  the  resistance  x,  has  two 
other  paths  open  to  it — through  contacts  C,  Cl  to  the 
brushes  of  the  small  regulating  motor  via  binding-posts 
R^D"  and  R3D3.  But  the  currents  in  these  two  circuits  are 
in  the  same  direction,  and  when  they  meet  at  the  regulating 
motor  they  oppose  each  other,  and  its  armature  remains 
stationary.  Thus  the  main  current  divides  into  three  parts 
where  A  is  in  normal  position. 


FIG.  94. — EXCELSIOR  ARC  DYNAMO  CONTAINING  MOTOR  TO  REGULATE 
BRUSHES.  THE  FRONTS  OF  THE  POLE  PIECES  SWING  OUT  ON  HINGES 
TO  GIVE  ACCESS  TO  ARMATURE. 

If  from  any  cause  the  current  increases  above  the  nor- 
mal, the  armature  A  of  the  wall-controller  is  drawn  away 
from  its  balancing  position,  breaking  the  contact  at  C,  while 
that  at  C1  is  still  maintained.  The  regulating  current  now 


OK   THi 


UNIVERSITY 


has  only  one  path  open  to  it  from  Cl  to  R9,  etc.,  to  the  left- 
hand  or  upper  brush  of  the  motor  regulator,  thence  partly 
through  the  armature  to  the  other  brush  and  out  to  line 
through  the  resistance  z*.  The  motor  armature  at  «once 
starts  to  revolve  and  to  turn  the  brushes  of  the  machine  in 
the  direction  for  cutting  down  the  current;  at  the  same 
time  a  rod  connected  to  the  brush-holders,  but  not  here 
shown,  acts  upon  a  field-switch,  which  assists  the  brushes  in 
reducing  the  current  by  cutting  out  sections  of  the  wire 
upon  the  field-magnets. 


D1  Dz  D3  &  D*  ARE  BINDING  POSTS  ON  DYNAMO 
R1  R2  R3  &  R*  ARE  BINDING  POSTS  ON  REGULATOR 


'  «  FIG.  95. — CONNECTIONS  OF  EXCELSIOR  DYNAMO. 

When  the  normal  current  has  again  been  established,  the 
controller  armature  closes  contact  C,  and  the  regulating 
motor  stops.  A  diminution  of  the  current  from  the  normal 
causes  the  breaking  of  the  contact  C1,  which  sends  the  regu- 
lating current  through  the  motor  in  the  direction  opposite  to 


2O2  Practical  Management  of 

that  just  described,  with  a  corresponding  effect.  It  is  evident 
that  at  all  times  the  resistances  x  and  either  y  or  z  are  in 
circuit ;  they  therefore  always  act  as  shunts  to  the  two 
points  c  and  c't  and  no  sparking  whatever  takes  place  when 
contact  is  broken  at  either  of  those  points. 

Thus,  with  any  variation  in  the  current,  not  only  are  the 
brushes  revolved  in  a  corresponding  direction  by  the  regu- 
lating motor,  but  the  field-switch  is  operated,  to  cut  sec- 
tions in  or  out,  by  means  of  the  connecting  arm  ;  both  these 
methods  of  regulation  acting  in  conjunction  serve  to  bring 
the  current  to  its  normal  value. 

A  switch  is  provided  for  the  purpose  of  cutting  out 
the  regulating  motor  when  adjusting  the  position  of  the 
magnets  M,  while  the  field-switch  mentioned  above  is  em- 
ployed for  short-circuiting  the  field-magnets  when  shutting 
down  the  machine. 


Dynamos  and  Motors. 


203 


CHAPTER  XXXIII. 
ARC-CIRCUIT   MOTORS. 

CONSTANT-CURRENT  or  arc-circuit  motors  all  have  me- 
chanical regulating  devices  for  controlling  their  speed  and 
power,  since  the  power  is  not  reduced  by  the  increase  of 
counter  E.  M.  F.  when  the  motor  speeds  up,  as  it  is  on 
circuits  of  constant  potential. 

Various  means  of  reducing  the  power  have  been  tried, 
the  most  common  being  a  switch  arranged  to  reduce  the 
strength  of  the  magnets.  Such  are  the  Excelsior,  Brush, 
Baxter,  and  "  C.  &  C."  machines  (Fig.  96).  The  switch  is 


FIG.  96. — "C.  &  C."  ARC  MOTOR,  ILLUSTRATING  ALL  THOSE  HAVING  A 
CENTRIFUGAL  GOVERNOR  OPERATING  A  SWITCH  TO  VARY  THE  FIELD 
STRENGTH. 

connected  to  a  centrifugal  speed-governor,  so  as  to  cut  out 
the  magnet-winding  as   the    speed   increases.     The  objec- 


204  Practical  Management  of 

tions  to  this  arrangement  are  that  the  weakening  of  the  fields 
tends  to  cause  sparking,  and  the  sluggishness  of  the  mag- 
nets prevents  the  changes  of  strength  being  effected  in  time 
to  prevent  the  motor  racing  for  a  moment  when  the  load  is 
thrown  off,  and  vice  versa. 

The  regulator  is  arranged  to  be  operated  by  hand  (Fig. 
97)  when  it  is  desired  to  vary  the  speed  from  time  to  time, 


FIG.  97. — CROCKER- WHEELER  ARC  MOTOR  WITH  HAND  REGULATOR. 

as    in    running  sewing-machines ;  but  this  is   usual   only  in 
small  motors. 

To  overcome  the  objections  to  the  methods  of  control 
just  described,  the  plan  of  rotating  the  brushes  from  the 
position  of  full  power  to  that  of  no  power  is  also  used  (Figs.  97 
and  98).  The  brushes  are  moved  in  the  direction  which  will 
bring  the  magnetism  of  the  armature  into  opposition  to  that 
of  the  field  by  degrees  so  that  both  are  reduced  equally, 
which  prevents  the  weakened  field  causing  sparking;  and 
since  the  power  is  reduced  by  the  change  of  position  of  the 
brushes,  there  is  no  loss  of  time  on  account  of  sluggishness 
of  the  magnets.  This  can  only  cause  momentary  sparking 
in  the  interval  before  the  fields  are  weakened  by  the  arma- 
ture reaction.  The  difficulty  in  this  machine  is  the  me 


Dynamos  and  Motors. 


205 


chanical  one  of  moving  the  brushes,  maintaining  the  cable 
connections,  etc.  The  governor  has  to  be  rather  large,  to 
secure  close  speed  regulation. 

In  all  these  forms  the  only  special  points  are  in  the  care 
of   the    governor.      The    motors    are    simple    series-wound 


FIG.  98. — CROCKER-WHEELER  ARC  MOTOR  WITH  CENTRIFUGAL  GOVERNOR 
TO  ROTATE  BRUSHES. 

machines,  such  as  treated  in  Part  I.  Those  which  regulate 
by  a  switch  are  liable  to  troubles,  because  the  switch  or  the 
connections  from  the  switch  to  the  coils  get  out  of  order. 

In  the  brush-revolving  form  the  brushes  may  jump  off 
the  commutator  an  instant  when  moved  suddenly  by  the 
governor,  if  they  are  not  properly  adjusted.  Or  they  may 
not  make  perfect  contact  in  all  positions  of  the  rocker- 
arm  if  it  does  not  turn  around  the  commutator  truly;  that 
is,  the  brushes  may  be  held  straight  when  on  top  of  the 
commutator,  and  crooked  when  at  the  side. 

In  any  form  the  speed-governor  requires  attention.  A 
governor  which  is  "  quick "  or  isochronous,  that  is,  goes 
through  its  whole  motion  with  a  very  small  variation  of 
speed,  will  turn  on  too  much  power  when  the  load  and 
speed  are  only  slightly  varied,  thus  overdoing  the  regulation 


206          Practical  Management  of  Dynamos  and  Motors. 

and  causing  the  motor's  speed  to  fluctuate  up  and  down 
constantly.  On  the  other  hand,  one  that  is  "  slow,"  or  only 
goes  through  its  whole  motion  when  the  speed  varies  one  or 
two  hundred  revolutions,  will  allow  the  motor  to  run  slow 
under  heavy  load  and  fast  under  light  load. 

Most  governors  are  capable  of  adjustment,  and  should 
be  adjusted  to  be  as  "  quick "  as  is  consistent  with  the 
nature  of  the  load.  Sometimes,  when  close  regulation  is  re- 
quired, the  governor  is  set  to  be  sensitive  or  quick,  and  a 
fly-wheel  is  also  used  on  the  motor  (Fig.  99)  or  driven  machine 
to  steady  the  variations  of  load. 


FIG.  99.— EXCELSIOR  ARC   MOTOR  WITH   FLY-WHEEL,  AND  CENTRIFUGAL 
GOVERNOR,  OPERATING  FIELD-SWITCH. 

When  the  full  power  is  exceeded,  an  arc  motor  will 
slow  down,  and  then  increasing  the  load  or  even  leaving  it 
overloaded  will  only  reduce  the  power  obtained. 


THE  END. 


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THOMPSON,  Prof.  S.  P.  Dynamo-electric  Machinery.  With  an  Intro 
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<  No.  66  Van  Nostrand's  Science  Series.)  .................................  $0.5 

—  -  —  Recent  Progress  in  Dynamo-electric  Machines.  Being  a  Supplement  to 
"  Dynamo-electric  Machinery."  Illustrated.  12mo,  cloth.  (No.  75  Van 
Nostrand's  Science  Series.)..  .  ....................  »  ................  .....  $0.50 

-  —  The  Electro-magnet  and  Electro-magnetic  Mechanism.  213  Illustrations. 
8vo,  cloth  ..............  .  ...........................................  ...$6.00 

TREVERT5  E.  Practical  Directions  for  Armature  and  Field-magnet 
Winding,  12mo,  cloth.  Illustrated  ...........  ....  ......................  $1.50 

TUMLIRZ,  Dr.  Potential,  and  its  application  to  the  explanation  of  Elec- 
trical Phenomena.  Translated  by  D.  Robertson,  M.D.  12mo,  cloth  —  $1.25 

TUNZELMANN,  G.  W.  de.  Electricity  in  Modern  Life.  Illustrated. 
12mo,  cloth  ............................................................  $1.25 

URQITHART,  J.  W.  Dynamo  Construction.  A  Practical  Hand-book  for 
the  Use  of  Engineer  Constructors  and  Electricians  in  Charge.  Illustrated. 
12mo,  cloth....  ,  .......................  ...  .......  .....  .................  $3.00 

WALKER,  FREDERICK.  Practical  Dynamo-building  for  Amateurs. 
How  to  Wind  for  any  Output.  Illustrated.  16mo,  cloth.  (No.  98  Van  Nos- 
strand's  Science  Series.)  ..................................................  $0.50 

WALKER,  SYDNEY  F.  Electricity  in  our  Homes  and  Workshops.  A 
Practical  Treatise  on  Auxiliary  Electrical  Apparatus.  Illustrated.  12mo, 
cloth  ...................................  .  .....................  .  .........  $1.50 

WEBB,  J.  Li.  A  Practical  Guide  to  the  Testing  of  Insulated  Wires  and 
Cables.  Illustrated.  12mo,  cloth  .................................  ,....$1.00 


F.  MARTEN.  Drum  Armatures  and  Commutators. 
(Theory  and  Practice.)  A  complete  treatise  on  the  theory  and  construction 
of  drum-winding,  and  of  commutators  for  closed-coil  armatures,  together 
with  a'  full  resume,  of  some  of  the  principal  points  involved  in  their  design; 
and  an  exposition  of  armature  reactions  and  sparking.  8vo,  cloth.  Illus- 
trated ..............  ,  ..............  .  ..............  .  .  ......................  $3.00 

WORMELLi,  R.  Electricity  in  the  Service  of  Man.  A  Popular  and  Prac- 
tical Treatise  on  the  Application  of  Electricity  in  Modern  Life.  From  the 
German,  and  edited,  with  copious  additions,  by  R.  Wormell,  and  an  Intro- 
duction by  Professor  J.  Perry.  With  nearly  850  Illustrations.  Royal  8vo, 
cloth  .....  .  ..............  .  ................  .  .............  . 


***  A  General  Catalogue    64  pages— of  Work*  la  all  branches 
of  Electrical  Science  furnished  gratis  on  application. 


CJNIVEKSITY 

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